Top 12 Police Mistakes in a DUI Investigation

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

In this post your going to learn how police officers can make mistakes in a DUI investigation which can impact the outcome of a case.

In fact:

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.

And today I am going to show you how we spot police mistakes…

…and you can do the same thing.

1. Insufficient Reasonable Suspicion For Investigative Stop

Before police can stop you on suspicion of DUI 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.

Is Reasonable Suspicion A Lower Standard Than Probable Cause?

The standard is less than that of arresting you based on probable cause since the detention is minimal, at least at first2.

Does An Officer Have To State Why You Were Pulled Over In His/Her Police Report?

An officer stops your vehicle, the officer must state in his/her report why you were stopped.

  • You were speeding,
  • You had unlawfully or unsafely changed lanes,
  • You failed to make a complete stop at a stop sign
  • You are observed to be weaving in a traffic lane
  • You are sleeping at the side of the road, or
  • Engaged in conduct that may be unsafe or committed any other vehicle code violation or infraction

It is not necessary that the officer suspects that you are under the influence.

If the officer stated that he/she stopped you simply based on this feeling or hunch, it would be grounds for exclusion of all evidence obtained as a result of the illegal stop.

Stops at Checkpoints

Does An Officer Need Reasonable Suspicion To Pull You Over At A Checkpoint?

An officer does not need reasonable suspicion or probable cause to pull you over at a checkpoint provided the guidelines in Ingersoll v Palmer are followed3.

An officer is permitted to stop and observe certain vehicles according to a specific protocol and determine if the motorist may be under the influence and/or properly licensed.

2. Failure to Obtain a Drinking Pattern

Your drinking pattern can be instrumental in determining whether your BAC test results were accurate. If your blood alcohol concentration is still rising, then the result on the breath test is not necessarily indicative of what your bac was at the time of driving.

Under the law, it is a rebuttable presumption that you were under the influence if your BAC is 0.08%4.

Police Failure To Obtain Statements Can Be Detrimental to The Prosecutions Case

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.

3. 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 manyof 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 nine (9) steps, turn on one foot, keep your hands at your side, count out the steps, look at your feet, and return in the same manner.

When performing this test, you are required to recall all of the instructions. If you fail the following:

  • Keep your balance
  • Take the wrong number of steps
  • Fail to walk heel to toe
  • Lift your hands to balance
  • Step off the line
  • Stop while walking
  • Perform an improper turn

Then this will be noted by the officer as an indicia of impairment.

What If The Officer Gave You Incorrect Instructions For The Walk And Turn Test?

If the officer gave you incorrect instructions then the test is considered less reliable as an indication of your impairment.

One Leg Stand

For 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.

Any hopping or swaying at your sides can be interpreted as impairment.

If the police officer instructed you incorrectly then that will affect the reliability of this test to be used as evidence by the prosecution of your intoxication

Horizontal Gaze Nystagmus

For this test, the officer will hold up a finger or pencil 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.

4. 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 proximity5.

Why Does An Officer Need To Observe You For 15 Minutes?

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.

Officers routinely violate this directive in a variety of ways.

Examples Of A Violation of The 15 minute Observation Period

  • 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 results6.

How Does Officer Failure To Wait 15 Minutes Affect Your Case?

While the lack of constant observation may not result in the 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.

5. Failure to Keep Track of Important Details

Prosecutors are tasked with the burden of proof in any criminal case.  In DUI cases, the details are important in establishing the reliability of the BAC presented as proof of impairment.

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.

General Alcohol Concentration Curve

  • Y: Alcohol Concentration

Prosecutors are tasked with the burden of proof in any criminal case.  In DUI cases, the details are important in establishing the reliability of the BAC presented as proof of impairment.

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.

What Happens If Your BAC is Still Rising?

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.

Impact Of Food On Alcohol Absorption

  • Empty Stomach
  • Full Stomach

Prosecutors Rely On Police Officers To Get The Details

Police officers err when they fail to produce statements 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.

How Do You Use This To Your Advantage?

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 driving7.

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.

How Do You Prove Your Drinking Time?

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.

6. 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. These requirements are outlined in Title 17 of the California Code of Regulations and help ensure that the results are accurate.

What Is An Example Of An Unreliable Test Result?

If your first breath test was 0.08% and your second was 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.

What Is An Example of A Police Error?

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 as valid.

7. Failure to Properly Admonish in A Chemical Test Refusal

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 chemical test when stopped for a DUI8. The admonishment is printed on the back of the DS 367 so that the officer can read it directly from the DS 367 to the driver.

What Is The Admonishment?

The officer must clearly explain the following:

  • The chemical test is required by law
  • Available tests have been offered to you
  • Refusal to take a chemical test or failure to complete a test will result in the following consequences
    • A one-year license suspension, or
    • A two-year license revocation with a prior DUI conviction
    • A three-year license revocation with two or more prior DUI or wet reckless convictions

What Are The officer’s Requirements With Regard To The Admonishment?

  • The driver must be able to clearly hear the admonishment. If there was noise which prevented the driver from clearly hearing the admonition and the officers were aware of it then the driver was not properly admonished9.
  • The admonition must be read from the DS 367 or an approved form, the officer may not change language within the admonition which might mislead the driver10.
  • The admonition must be read by a peace officer

What Happens If The Officer Failed To Admonish You Properly?

If the officer neglected to read the admonishments as required under law, your license should survive suspension. Alternatively, if the officer gave you the incorrect time period for your license suspension it may be reduced to a lower time period if that was the time period that the officer admonished you with11.

8. 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.

A prosecutor must demonstrate in whose custody the sample was at all times and that it was properly labeled and stored.

Documentation must be rigorously followed from the time of collection until disposal.

Why Is The Chain Of Custody Important?

A blood sample for DUI or any other evidentiary purpose cannot be introduced at trial unless a proper foundation is laid.  The prosecution must be 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.

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.

What Happens If The Chain of Custody Was Broken?

If the chain of custody is interrupted which means that the evidence was not transported and booked in accordance with protocol 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 contaminated12.

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.

9. 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.

What is the Purpose of This Advisement?

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 tested with a blood split order or urine sample tested. This advisement is known at the Trombetta advisement13.

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.

10. 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 consent14. 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 201315. 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 defendant16.

11. 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.

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

What Happens If The Pas Was Not Turned In For Testing?

Failing to turn in the PAS device for accuracy testing calls into question the accuracy of the BAC test result. 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.

This Violation Goes To The Weight Of Evidence Not Admissability

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 results17. However, your attorney should make a motion to exclude the results in any event.

A violation of Title 17 goes to the weight of the evidence18. 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.

12. 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.

Why Would A Police Officer Copy/Paste A 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 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 conduct19.

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. People v. Gallardo (1994) 22 Cal.App.4th 489, 496 []
  5. Manriquez v. Gourley (2003) 105 Cal.App.4th 1227 []
  6. People v. Adams (1976) 59 Cal.App.3d 559, 567 []
  7. People v. Roder (1983) 33 Cal.3d 491, 497-505 []
  8. 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. []
  9. Thompson v. DMV, 1980 107 Cal.App.3d 354 []
  10. Giomi v. DMV, 1971 15 Cal.AppJd 905 []
  11. Daly v DMV, 1986 187 Cal.App. 3d 259 []
  12. People v. Lucas (1995) 12 Cal.4th 415, 444; People v. Herrera (2000) 83 Cal.App.4th 46, 61 []
  13. California v. Trombetta (1984) 467 US 479 []
  14. Schmerber v. California (1966) 384 US 757 []
  15. Missouri v. McNeely (2013) 133 S.Ct. 1552 []
  16. Rochin v. California (1952) 342 US 165; US v. Miller (1989) 891 F.2d 1265 []
  17. People v. Adams (1976) 59 Cal.App.3d 559; People v. Bury (1996) 41 Cal.App.4th 1194 []
  18. People v. Williams (2002) 28 Cal.4th 408, 417 []
  19. Pitchess v. Superior Court (1974) 11 Cal.3d 531 []

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