Top 12 Police Mistakes in a DUI Investigation

This Article Explains Officer Mistakes That Could Sway The Outcome Of A Case

Police officers can make mistakes in a DUI investigation which can impact the outcome of the court case.  Should the police fail to follow certain procedures, a motion to exclude or suppress incriminating evidence or to dismiss the charges against you can be filed. Below is a list of Aizman Law Firm’s top twelve mistakes we’ve seen police officers make in DUI investigations.

Insufficient Probable Cause for A Stop or Arrest

Before police can stop you on suspicion of DUI, or for any other matter, the officer must have reasonable suspicion to do so. Reasonable suspicion in this context is having reasonable grounds or that the officer can point to specific articulable facts for suspecting that you are violating the law1. The standard is less than that of arresting you based on probable cause since the detention is minimal, at least at first2.

So when an officer stops your vehicle, the officer must state in his/her report that you were speeding, had unlawfully or unsafely changed lanes, failed to make a complete stop at a stop sign, or committed any other vehicle code violation or infraction. An officer can also stop you if you are observed to be weaving in a traffic lane, sleeping at the side of the road, or otherwise engaged in conduct that may be unsafe. It is not necessary that the officer suspect that you are under the influence.

It is rare for an officer to state in a report or in a court proceeding that you were stopped because he or she had a feeling you were drunk without pointing to certain actions on your part that would suggest impairment. Furthermore, if the officer stated that he/she stopped you simply based on this feeling or hunch, it would be grounds for an exclusion of all evidence obtained as a result of the illegal stop.

Stops at Checkpoints

Other stops are at roadside or DUI checkpoints. These are legal in California, provided certain guidelines are followed3. An officer is permitted to stop and observe certain vehicles according to specific protocol and determine if the motorist may be under the influence and/or properly licensed.

Probable Cause for Arrest

Once you are stopped, the police officer can begin a DUI Investigation provided he or she believes you may be driving while under the influence. Again, the officer must be able to point to specific, articulable facts that would lead a reasonable officer to believe that you are under the influence. The standard for arresting you for DUI, however, is stronger than that of mere suspicion as the officer must state these facts with specificity and possess “ honest and strong suspicion that the person is guilty of a crime”4.

There are many indications of intoxication that an officer could articulate:

  • You have a odor of alcohol on your breath
  • You are slurring your words
  • There is an open bottle or other container of alcohol in plain view
  • You exhibit watery, bloodshot eyes
  • You lack basic coordination in balance or walking
Field Sobriety Tests

If the officer detects these common objective signs of intoxication, you may be asked to perform FSTs, or field sobriety tests, or to take a PAS, or preliminary alcohol screening test. This is a mobile breath test that can provide an “articulable fact” leading the officer to investigate further.

Your poor performance on these tests will inevitably lead the officer to ask that you submit to a breath or blood test. All motorists, except for those under age 21 or who are under probation, are not legally obligated to submit to an FST, to answer questions about drinking, or to take the PAS. Unless you are one of these exceptions, then there are fewer facts for the officer to point to, or even less than probable cause, to believe you were driving under the influence.

Refusing A Breath test

If you refuse testing, the officer can still arrest you and will state that you exhibited other objective symptoms of intoxication or impairment. A refusal can also be used at trial against you as consciousness of guilt, or that if you had submitted to testing, your BAC would have been at or above 0.08%, the level at which you are presumed under the influence.

Other Examples of No Probable Cause

A scenario where an officer lacks probable cause to arrest you for DUI may occur where you are found outside the vehicle or in another location from your car. For instance, the officer tracks your license plate based on a witness’ testimony or from your license plate on your abandoned vehicle to your residence where the officer observes you to be under the influence.

In this case, so long as you do not admit to having been drinking heavily just prior to driving, it is just as likely you were drinking at home and not just before driving. Accordingly, there is no probable cause to arrest you or there is at least insufficient evidence that you were under the influence while driving.  Many factors can affect the probable cause requirement in this instance.  For example:  if you were involved in an accident and the other driver is able to positively ID you as having been driving at a specific time, the officer may be able to obtain probable cause based on these other factors in totality.

Establishing The Driver

Another situation is where you are standing outside your vehicle with other people when police first come into contact with you. If no one admits to driving, then there is no probable cause to arrest you, even if the car is registered to you. In some cases, an officer may arrest you in any event since you are the owner.

In those situations, your attorney should review the totality of the evidence in determining the likelihood of success in a motion to suppress the evidence because of an illegal arrest.

Failure to Obtain a Drinking Pattern

Your drinking pattern can be instrumental in determining whether your BAC test results were accurate, especially if your result is at 0.08% or even if it is considerably higher when there other evidence exists that strongly suggests that you were not impaired. Under law, it is a rebuttable presumption that you were under the influence if your BAC is 0.08%5.

Failure To Obtain Statement

Police officers as well as prosecutors often err when they fail to produce statements or testimony that shows how many drinks you had and when you had your last drink so as to refute your argument that your BAC was at a legal level when you were driving. You can demonstrate your drinking period over an approximate time through receipts from the establishment where you were drinking and/or from testimony of a bartender, waitress or other witness to your drinking who can also attest that you exhibited no signs of intoxication when you left.

Prosecutor Use of Retrograde Extrapolation

Prosecutors rely on expert testimony from toxicologists that are tasked with estimating your BAC at the time of driving.  Often times, the chemical test is taken several hours after the alleged time of driving.  The prosecutor must prove what your BAC was at the time of driving, rather than just at the time of the test and they do this by having their expert calculate your BAC based on the time of your last drink. Prosecutorial experts will typically use retrograde extrapolation for this calculation.

Incorrect Administration of Field Sobriety Tests (FST)

When a motorist is pulled over for a traffic or equipment violation, and the officer suspects the driver has been drinking, he or she often requests the driver to perform certain field sobriety tests. There are 3 tests which have been standardized by the National Highway Traffic Safety Administration (NHTSA):


Walk and turn


One-leg stand


Horizontal Gaze Nystagmus

These are designed to demonstrate that the motorist’s coordination and/or ability to follow instructions has been impaired by alcohol. In the majority of these tests, the investigating officer incorrectly administers these tests.

Walk & Turn

There are a number of instructions that an officer is supposed to give for correctly performing this test. For instance, you are to walk heel to toe on a line for a certain number of steps, turn a certain way, keep your hands at your side, count out the steps, look at your feet, and return in the same manner.

Most people when detained by police are under extreme stress and are generally tired since most DUI arrests take place in the evenings. Also, many individuals suffer from joint or back problems and are unable to satisfactorily perform most so-called coordination tests under the best of circumstances.

When performing this test, you are required to recall all of the instructions. If you fail to walk heel to toe, lift your hands while walking or forget to count out loud, this will be noted by the officer as an indicia of impairment. Of course, remembering all of these instructions, especially when given quickly by the officer, is extremely difficult under any circumstances. An officer will also rarely keep reminding you of the instructions given.

One Leg Stand

Unless you have better than average balance, be prepared to fail this test. You are required to stand on one foot for up to 30 seconds and to count each second off. Keep each leg straight and arms at your sides. Even discounting the fact that you are under considerable pressure, any hopping or swaying at your sides can be interpreted as impairment.

Horizontal Gaze Nystagmus

For this test, the officer will hold up a finger, pencil or other stimulus in front of your face and tell you to track it while observing your eye movements. The officer is looking for involuntary jerking of the eyes called nystagmus.  This test is often improperly administered and officers do not account for the natural nystagmus that occurs in persons who are not impaired.

Studies of these tests have shown that they are not reliable indicators of impairment and that officers in the majority of cases fail to conduct them properly. Such tests may are not administered correctly for several reasons, including not accounting for these factors:

  • Sloped surface
  • Windy conditions
  • Physical condition of the suspect other than from intoxication

Other FSTs include reciting the alphabet, performing finger to nose, counting backwards, standing with feet together and tipping your head backwards while estimating 30 seconds in your head with closed eyes, among others.

Instructions are usually given rapidly and suspects are more than likely to forget something. Another problem is that an officer has no way of knowing how the suspect would have performed the test regardless of how much alcohol the person had performed or under any other circumstances.

Failure to Wait 15 minutes for Breath Test (Title 17)

Under Title 17 CCR §1219.3, an officer is required to place you under constant observation for 15 minutes before the breath test is administered. The officer does not have to have eyes on you the entire time but need only be in close proximity6. The purpose of the observation is to ensure the suspect does not eat, drink, vomit, regurgitate, burp, belch, or smoke. Any of these actions can affect the results of the breath test, usually with a false high BAC result.

Officers routinely violate this directive in a variety of ways. When transporting a suspect to a police station to administer the breath test, a suspect may be in a caged back seat, sprawled on the seat, or otherwise not within the observation of the officer. At the police station, the suspect may be left alone for several minutes while preparation is made for conducting the test. Further, the officer may have failed to note an entry about when the 15-minute observation period began. Your dui defense attorney can certainly argue that the officer’s failure to follow Title 17 directives unduly influenced the test and cast reasonable doubt on the results7.

While the lack of constant observation may not result in suppression of the test results, it can certainly go to the weight of the evidence. An officer can certainly testify regarding the reason or purpose of the rule since if the suspect did eat something, belched or burped, or vomited at all, it can affect the test results.

Failure to Keep Track of Important Details

When people drink alcohol, their BAC will rise while they are still absorbing the alcohol they have consumed. This means that if you just consumed alcoholic beverages and then begin driving a few minutes later, your BAC may not be at the 0.08% level because your body may not have absorbed all of the alcohol consumed. However, if you are stopped and investigated for suspicion of DUI and take a breath or blood test an hour or so after you were stopped, then your BAC may have risen to 0.08%. while you were out of your car. This is also referred to as the “Rising Blood Alcohol Defense.”

Alcohol is absorbed into the body at different rates and depends on an individual’s physiology, metabolism, and if there is food in the stomach. The timing of when you last consumed an alcoholic beverage and when you ate can have a substantial effect on how the alcohol you drank enters your body and at what rate it is absorbed.

For instance, after you are pulled over and asked to take a breathalyzer, you may still be absorbing the alcohol. In this case, your BAC will still be on the rise so that the breath test results will show a higher BAC level than when you were driving.

Under California Vehicle Code Section 23152(b), it is unlawful to drive with a BAC of 0.08% or higher. There is a rebuttable presumption that a BAC test result obtained within 3-hours of driving is your BAC when you were driving8.

Your defense attorney can rebut this presumption with credible expert testimony from a forensic toxicologist who takes the time of your consumption of alcohol and food and demonstrates that your BAC was on the rise when you were tested an hour or more after you actually drove and show that your BAC was below 0.08% while you were driving.

Police officers as well as prosecutors often err when they fail to produce statements or testimony that indicates when you had your last drink so as to counter your argument that your BAC was at a legal level when you were driving. Again, you can show an approximate time when you were drinking through receipts from the establishment where you were drinking or from testimony of a bartender, server or other witness to your drinking.

Not Obtaining 2 Breath Samples

When you are given the breathalyzer, the operator is required to obtain two breath samples whose results do not differ by more than .0.2 grams per 100 liters of blood alcohol. For example, if your first breath test was 0.08% and your second is 0.12%, it is not a valid sample. If this occurs, the officer or operator must conduct another test or tests so that two of them are within 0.02 grams of each other. The tests need not be consecutive. These requirements are outlined in Title 17 of the California Code of Regulations.

Errors by operators occur when they fail to notice that any two test samples are within the required 0.02 grams but submit the results nonetheless as valid, or require that the suspect take a DUI blood test as an alternative. If a blood test is given, it may be outside the 3-hour time when a motorist’s BAC result is presumed to be that of when the motorist was driving. If so, your dui attorney may move the court to exclude the results of the breath test or, if denied, argue that there is reasonable doubt over their accuracy.

Failure to Properly Admonish in A Chemical Test Refusal

According to the state’s implied consent law, every motorist in the state impliedly consents to having a breath or blood test taken to measure their blood alcohol concentration (BAC) level if the investigating officer has probable cause to believe the driver is under the influence.

If you refuse testing, there are certain consequences. The major one is that your driver’s license will be suspended for one year without the opportunity for a restricted license. You also face increased fines and sentencing penalties. At trial, the prosecution can argue that your refusal can be construed to mean that if you had submitted to a breath test, the result would have shown you were under the influence.

However, you can refuse testing if your refusal was reasonable under the circumstances or if the officer failed to properly admonish you. There is mandatory language contained in California Vehicle Code § 23612 whereby an officer is required to admonish you of the consequences of refusing to take a test9:

  • You face a fine
  • You will lose your license for one year for a first offense
  • You face mandatory jail time if convicted of DUI
  • You do not have a right to speak to an attorney prior to taking a test
  • That your refusal to take the test can be used against you in court (shows consciousness of guilt)

For any number of reasons, an officer may either forget to read the admonishments or figure that it is unnecessary. Many arrests and admonitions are recorded from the stop to the time when the officer asked you to submit to testing. If the officer neglected to read the admonishments as required under law, your license should survive suspension. Also, without a test result or a refusal, some prosecutors will agree to a plea bargain that is substantially lower than it would have been if they had this evidence.

Not Maintaining Chain of Custody in a Blood Draw

When a blood test is performed in a DUI case, the sample is required to be taken in a certain manner, marked or identified, and kept securely in an area where it will not be exposed to contamination. Documentation must be rigorously followed from the time of collection until disposal.

A blood sample for DUI or any other evidentiary purpose cannot be introduced at trial unless a proper foundation is laid and the prosecution is able to trace from competent evidence where the sample has been at all times from the time it was taken from the defendant to the time it was analyzed and to the present.

A prosecutor must demonstrate in whose custody the sample was at all times and that it was properly labeled and stored. In some cases, the sample is handled by multiple individuals and all must be identified and the times when the sample was in their custody. For instance, the sample may have been handled by the arresting officer, a medical technician or physician, the transporting officer, a person in charge of collecting and storing evidence at the lab, and possibly a chemist. The person who took the blood sample is generally responsible for labeling it and placing it in the container before storing it.

If the chain of custody is interrupted, then your defense attorney can move the court to suppress or exclude the sample from trial because it has not been established that the sample was the defendant’s or that it has been contaminated10.

If the court refuses to grant a motion to suppress, your attorney can still argue that the chain of custody was broken, thus injecting reasonable doubt about your guilt.

Failure to Provide a Trombetta Advisement

Under Vehicle Code § 23614, you are supposed to be advised before and after you submit to breath testing that the breath sample is not preserved, and that you have the opportunity to have a blood or urine sample taken from you at no cost to you. The purpose of this admonition is so you will have something that can later be analyzed to determine your BAC. Either you or the prosecution can have the subsequent blood or urine sample tested. This advisement is known at the Trombetta advisement11.

In many DUI arrests where a breath sample is taken, the officer omits this advisement. But under California law, this omission does not result in suppressing the results of the breath sample, However, your attorney can argue that this advisement is part of California law and was meant to protect defendants who contend that the breath test is subject to numerous influences that affect its results and that a blood test is more accurate. Further, your attorney may argue that the officer’s failure to so advise you deprived you of a right to a more accurate representation of your BAC. Introducing other evidence of a drinking pattern, your lack of signs of impairment, and the rising alcohol defense in conjunction with the officer’s failure to give you the Trombetta advisement can raise reasonable doubt in the minds of jurors.

Failure To Obtain Warrant Prior to Forced Blood Draw

For many years, police were permitted to force a defendant to have blood drawn in certain cases, Usually, these cases involved fatal DUI crashes where commercial drivers, as well as those with regular licenses, were suspected of being under the influence. Prosecutors argued that exigent circumstances existed in such cases that allowed them to extract a sample absent a warrant to do so if the defendant refused consent12. The rationale was that it took too much time to secure a search warrant to take a blood sample, allowing the alcohol or BAC level to dissipate. The fact that alcohol dissipates was itself an exigent circumstance that justified the warrantless search.

This changed in 201313. In the McNeely case, the court ruled that current technology now allowed much faster means to obtain a warrant so that the exigent circumstance regarding dissipation of a suspect’s BAC level that previously existed was no longer valid. In other words, officers can now obtain a warrant electronically, giving them adequate time to do so.

Should an officer force a defendant to produce a blood sample, usually by restraining the individual against his will, then the officer’s failure to obtain a warrant should render the blood sample result inadmissible at trial. The officer’s outrageous conduct in restraining a suspect to force extraction of a blood sample could also be used to move the court to dismiss all charges against the defendant14.

Failure to Turn in PAS Device for Required Accuracy Testing (Title 17 Violation)

The PAS, or preliminary alcohol screening device, is a handheld monitor that an investigating officer often uses to establish a motorist’s BAC closest to the time of driving.

While a motorist who is 21 or over is not required to take the PAS, or any other field sobriety test, without consequences, drivers under 21 or who are on probation for a prior DUI conviction are required to take the PAS or will face loss of driving privileges for 1 to 3-years depending on whether you have past convictions. In addition to the DMV  consequences of reusing the PAS while on DUI probation, it may also be an internal violation of probation to decline the PAS while on DUI probation.  By law, an officer is obligated to advise you that taking the PAS is optional, unless you fit one of the exceptions, though officers will generally present this as non-optional or will tell you that they just want to “make sure you’re ok to drive” before letting you go.

The results of a PAS are admissible at trial and can used to establish that you were under the influence and had a BAC of at least 0.08% in violation of the law. However, if the records kept by the particular police agency that has custody of the PAS device failed to have it tested for accuracy or maintained every 10 days or 150 uses (whichever happens first), this a violation of Title 17 of the California Code of Regulations.

Under Title 17, the officer administering the PAS is required to check or perform the following:

  • Ensure the PAS has been properly maintained and checked for accuracy every 10-days or after 150 uses
  • See that the device’s battery is charged
  • That it is not affected by RFI (radio frequency interference)
  • That the device has an internal operating temperature within standards or limits
  • Ensure that a new and sanitary mouthpiece has been affixed to the device before the first and subsequent blows
  • That a 15-minute observation period is followed before the defendant blows into the PAS
  • That 2 breath samples be obtained that are within 0.02 grams of each other and that there was a 2-minute reset between attempts
  • Conduct an “air blank” or reset the device so that it goes through a set sequence to verify there is no residual air from previous uses

Should the officer be unable to verify that the PAS was checked for accuracy either every 10 days or after 150 uses, then the results should be at least questioned regarding accuracy. Before the results of the PAS are introduced at trial, the prosecutor must lay a proper foundation for its admissibility. Your defense attorney can rebut the results with affirmative evidence that the guidelines were not followed.

The failure of an officer to follow all Title 17 provisions regarding the PAS test results will not necessarily result in a court excluding its results15. However, your attorney should make a motion to exclude the results in any event.

Otherwise, the violation of Title 17 goes to the weight of the evidence16.Your defense attorney can certainly argue that the purpose of the Title 17 provisions is to ensure the accuracy of the test results so that innocent persons are not wrongly convicted of DUI. If anything, the failure to follow Title 17 injects another element of reasonable doubt into your case.

Copy/Paste Police Report Without Changing Facts

Many police officers are diligent in preparing police reports that present the facts and circumstances of a vehicle stop, that all procedures were followed, and that probable cause was found for the stop, detention and arrest. However, there are times when an officer takes a short-cut in preparing the report. This may be done out of time constraints, fatigue, or laziness. A short-cut may be simply copying content from a different but similar stop and arrest case and pasting it into a current case that the officer has just investigated and without changing the facts specific to the arrest. In other words, filing the report without changing the narrative but only the names of the defendant or officers involved.

In these cases, an officer will use a similar report that has the same justification for stopping a vehicle, contains the same admonitions required to be given to the motorist when field sobriety and the BAC tests are requested, and sometimes with the same results. Because some officers may have been disciplined in the past or had prior complaints of copying and pasting police reports, your attorney can file a Pitchess Motion to request the investigating officer’s personnel file to determine if he or she was disciplined for such conduct17. In some cases, the officer who prepared the report might have forgotten to change a name or left in in an essential fact, such as the location of the stop, that will cast suspicion on the report’s accuracy.

Next Steps If You Need Help

If you have been arrested and would like to learn more about how attorneys charge.

If you want to understand why its important to have an attorney represent you.

If you would like to discuss a pending case with an attorney contact the Aizman Law Firm at 818-351-9555 for a free confidential consultation.

Request A Free Consultation 818-351-9555 


  1. Terry v, Ohio (1968) 393 US 1 []
  2. Probable cause for arrest is defined as “…only when the facts known to the arresting officer ‘would lead a man of ordinary care and prudence to believe and consciously entertain an honest and strong suspicion that the person is guilty of a crime.’” People v. Price (1991) 1 Cal.4th. 324,410 []
  3. Ingersoll v. Palmer (1987) 43 Cal.3d. 1321 []
  4. See People v. Price, supra. []
  5. People v. Gallardo (1994) 22 Cal.App.4th 489, 496 []
  6. Manriquez v. Gourley (2003) 105 Cal.App.4th 1227 []
  7. People v. Adams (1976) 59 Cal.App.3d 559, 567 []
  8. People v. Roder (1983) 33 Cal.3d 491, 497-505 []
  9. California Penal Code 23612(D) The person shall be told that his or her failure to submit to, or the failure to complete, the required chemical testing will result in a fine, mandatory imprisonment if the person is convicted of a violation of Section 23152 or 23153, and (i) the suspension of the person’s privilege to operate a motor vehicle for a period of one year, (ii) the revocation of the person’s privilege to operate a motor vehicle for a period of two years if the refusal occurs within 10 years of a separate violation of Section 23103 as specified in Section 23103.5, or of Section 23140, 23152, or 23153 of this code, or of Section 191.5 or subdivision (a) of Section 192.5 of the Penal Code that resulted in a conviction, or if the person’s privilege to operate a motor vehicle has been suspended or revoked pursuant to Section 13353, 13353.1, or 13353.2 for an offense that occurred on a separate occasion, or (iii) the revocation of the person’s privilege to operate a motor vehicle for a period of three years if the refusal occurs within 10 years of two or more separate violations of Section 23103 as specified in Section 23103.5, or of Section 23140, 23152, or 23153 of this code, or of Section 191.5 or subdivision (a) of Section 192.5 of the Penal Code, or any combination thereof, that resulted in convictions, or if the person’s privilege to operate a motor vehicle has been suspended or revoked two or more times pursuant to Section 13353, 13353.1, or 13353.2 for offenses that occurred on separate occasions, or if there is any combination of those convictions, administrative suspensions, or revocations. []
  10. People v. Lucas (1995) 12 Cal.4th 415, 444; People v. Herrera (2000) 83 Cal.App.4th 46, 61 []
  11. California v. Trombetta (1984) 467 US 479 []
  12. Schmerber v. California (1966) 384 US 757 []
  13. Missouri v. McNeely (2013) 133 S.Ct. 1552 []
  14. Rochin v. California (1952) 342 US 165; US v. Miller (1989) 891 F.2d 1265 []
  15. People v. Adams (1976) 59 Cal.App.3d 559; People v. Bury (1996) 41 Cal.App.4th 1194 []
  16. People v. Williams (2002) 28 Cal.4th 408, 417 []
  17. Pitchess v. Superior Court (1974) 11 Cal.3d 531 []

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