How Chain of Custody Issues Affect DWI Cases

Prosecutors win many Texas criminal cases with physical evidence collected at the scene of the crime or from the defendant after being taken into custody. The same is true of Houston DWI cases, which often hinge on blood or urine samples. To make sure this evidence is admissible, the prosecution needs to show it wasn’t tampered with.

In criminal cases, the prosecution specifically needs to prove it was collected, stored, and transported in ways that validate the integrity of the evidence. This is called proving the chain of custody. When there are problems with this chain—such as gaps or improper documentation—then reasonable doubt often arises that the evidence is corrupted or might not even implicate the defendant.

Our Houston DWI lawyers are experienced at scrutinizing the chain of custody. We can identify violations, emphasize reasonable doubt, and present your case to the jury. Contact us to find out whether we can help with your case.

Proper Documentation

Police must create a paper trail that shows how they collected evidence, transported it (such as to a lab), and stored it. This paper trail makes sense. Without sufficient documentation, no one will know that the blood sample tested for alcohol is really the defendant’s.

It could be anybody’s, so police need proper proof of when they collected the sample and how they kept it separate so that it wasn’t contaminated from other samples.

In DWI cases, the chain of custody most commonly applies to urine or blood samples which are tested for evidence of illegal drugs or alcohol. A proper chain of custody would identify the officer who collected the sample, along with the date and time. The officer would then hand it over to a technician, and this transfer should be properly documented as well.

Breaks in the Chain of Custody

The last thing the prosecution wants to see is a gap in the chain of custody. For example, your blood sample could have been transferred to a tech and then it ends up tested in a lab by a different technician. Here, there is no documentation of the sample being exchanged from one technician to the other.

When there are gaps, the possibility arises that the sample tested didn’t belong to the defendant. Maybe there was an accident switch. Or perhaps the police planted a sample and claimed that it was yours. The prosecution should be able to trace a sample back to you. If other evidence is used, it should be traced back to the crime scene or wherever it was collected.

Technicians can get sloppy with documentation. As a skilled and experienced Houston DWI law firm, we carefully review the chain of custody for all critical pieces of evidence. Where we see gaps or confusing information, we will highlight them to create reasonable doubt.

Contact Us Today

No one should be convicted based on shaky physical evidence, including blood draws that lack adequate documentation. Fortunately, the burden of proof is high enough that prosecutors need solid evidence to gain a conviction. For help with your case, call our legal team to schedule a free consultation. We can be reached at 281-280-0100 or click here for our law firm contact form.