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San Diego DUI Defense Attorney. Former Prosecutor explains common errors police make in a Driving under the influence investigation

by | Jun 16, 2020 | DUI, Firm News |

Every San Diego DUI case is different.  As a former prosecutor who has handled thousands of DUI cases, there are common errors that arise in DUI stops.  The key on a driving under the influence case is to first examine the case to determine if these errors exist.  Second, if there is an error, you want to be able to utilize that error to obtain the best possible outcome for the accused. 

Here are the most common errors:

  1. The Police did not have the grounds to stop you

Before the police can stop an individual they 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 law.  The officer should state in their report why someone was stopped.  Some examples of why police stop a person are:

  • Speeding
  • Unlawfully changing lanes
  • Weaving in a traffic lane
  • 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.  You want to examine the police report and videos to determine if the police had grounds to stop you.  Be proactive and contact the Law Offices of Mark Deniz at 858-751-4384.

2. Did the police administer a lawful DUI 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 followed.

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.

You want to carefully inspect the police documents to determine if the checkpoint was lawful.

3. Did the police obtain a valid drinking pattern?

Your drinking pattern can be instrumental in determining whether your blood alcohol level result was 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.  The failure to obtain statements can be detrimental to the prosecution’s 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 the testimony of a bartender, waitress or another witness to your drinking who can also attest that you exhibited no signs of intoxication when you left.  Contact the Law Offices of Mark Deniz at 858-751-4384 for a free consultation.

4. Does the Prosecutor need to use Retrograde Extrapolation to prove their case?

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.  Some important facts when using the theory are:

  • What time did police see you driving?
  • How much time passed from driving to the chemical test?
  • What was your BAC?

This formula is used by law enforcement expert witnesses to present a BAC that is rooted in several assumptions that may not be proven.  However, we present it to you as a way to demonstrate how the evidence against you will be presented by the prosecution team.  Be proactive and contact the Law Offices of Mark Deniz at 858-751-4384.

5. Did the police officer administer the Field Sobriety Tests correctly?

When a motorist is contacted by the police, and they suspect the driver has been drinking, they often request the driver to perform certain tests, called Field Sobriety Tests or FSTs.  There are 3 tests that have been standardized by the National Highway Traffic Safety Administration (NHTSA).  These tests provide the most validated information for the officer to form their opinion of whether someone may be DUI-driving under the influence.  The three tests are:

  1. Walk & Turn
  2. One-leg stand
  3. Horizontal Gaze Nystagmus

These are designed to demonstrate that the motorist’s coordination and/or the ability to follow instructions has been impaired by alcohol.

The key when examining the officer’s administering of these tests is to review both the videos and police reports. 

Walk and turn test

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 indication of impairment.

If the officer gave you incorrect instructions, or did not note the test accurately, 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 or did not note the test accurately, then the test is considered less reliable as an indication of your impairment.

Horizontal Gaze Nystagmus or HGN

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
  • The 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 (Rhomberg test).

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.

6. Adhering to Title 17 while administering the chemical tests

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 proximity.

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 are

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.

The Law Offices of Mark Deniz can certainly argue that the officer’s failure to follow Title 17 directives unduly influenced the test and cast reasonable doubt on the results.  Be proactive and contact the Law Offices of Mark Deniz at 858-751-4384.  While the lack of constant observation may not result in the suppression of the test results, it can go to the weight of the evidence.  An officer can 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.  Be proactive and contact the Law Offices of Mark Deniz at 858-751-4384.

7. The police fail to note 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.

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 a “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.  This includes food consumption as well.  If facts can demonstrate a BAC under .08% at the time of driving, it can expose the prosecution’s case.

8. Unreliable chemical test results

When you are given the breath test, the police officer is required to obtain two breath samples whose results do not differ by more than .02 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.

9.  Improper Admonishment on a Chemical Test Refusal DUI

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 San Diego DUI.  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.

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


  • The driver must be able to clearly hear the admonishment.  If there was noise that prevented the driver from clearly hearing the admonition and the officers were aware of it then the driver was not properly admonished.
  • 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 driver.
  • 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.  Be proactive and contact the Law Offices of Mark Deniz at 858-751-4384.

10. Not maintaining a proper Chain of Custody of a BloodTest

When a blood test is performed in a DUI case, the sample is required to be obtained 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 is 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 from jury trial because it has not been established that the sample was the defendant’s or that it has been contaminated.  Be proactive and contact the Law Offices of Mark Deniz at 858-751-4384.

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

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

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, the Law Offices of Mark Deniz may argue that the officer’s failure to do so 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.  Be proactive and contact the Law Offices of Mark Deniz at 858-751-4384.

12. Blatant Cut and Paste and Police using Police Report Templates

In my almost 10 years as a former Prosecutor, many police officers were 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 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 conduct.

In some cases, the officer who prepared the report might have forgotten to change a name or left in an essential fact, such as the location of the stop, that will cast suspicion on the report’s accuracy. Be proactive and contact the Law Offices of Mark Deniz at 858-751-4384.

13. Failing to Read Miranda Rights

According to the San Diego DUI laws, Miranda Rights should be read to you before being placed in custody.  The key is determining from the facts whether someone is in custody or not.  Police are able to conduct a DUI investigation (Berkemer v. McCarty). However, their actions may go past what they are able to do and Miranda Rights should of been read to the individual.  It is vital to examine police reports and videos to determine this.  The Miranda rights give you an option to remain silent, employ an attorney, or look for a public defender to represent you in case you cannot hire an attorney.  If the arresting officer doesn’t read out these rights, you can contest the evidence. There are circumstances when the motorists make implicating statements or admit that they were driving under the influence.  The comments may not be used as evidence against you, especially if the Miranda rights were not read to you during the arrest. 

Moreover, Miranda rights may have been read to you, but the police did not allow you to make a choice.  For instance, maybe you wanted to remain silent or be allowed an opportunity to look for an attorney.  If the police fail to give the options and go ahead into further interrogation, the law views it as illegal.  It is expected that any further questioning stops after you have made your choice.  As such, any incriminating statements beyond this limit are not taken as evidence.  

You want to get the best possible outcome in the case.  What do you do next?   Be proactive and contact the Law Offices of Mark Deniz at 858-751-4384.

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