Forensic evidence can seem almost impossible to dispute. A lab report, DNA result or expert opinion may lead you to believe the science has already settled the question. But even sound forensic methods can produce bad results. Errors can happen when someone handles evidence, runs a test or reads the results.
Here are some ways a defense attorney can find and challenge flaws in forensic evidence.
Checking how evidence was collected and handled
Contamination, transfer and poor handling can damage evidence before a lab ever tests it. DNA offers a good example. Finding your DNA at a scene does not always show when or how it got there.
A defense attorney can review how police collected, packed and stored the sample, including whether contamination or other handling errors could have affected the result.
Examining how forensic evidence was tested
A lab result depends on the methods used to test the evidence. With drug chemistry testing, an attorney can ask whether a forensic chemist used the right method, maintained the equipment and followed testing rules.
Ballistics tests also show why the testing process matters. A firearms examiner may compare markings on a bullet or cartridge casing to determine whether they came from a particular firearm. A defense attorney can examine whether that comparison supports the examiner’s conclusion.
Questioning what the results actually show
The data may not support the full claim that prosecutors make to a jury. For example, a cell tower expert may use phone records to identify the towers and sectors that handled a call or data connection. That can show an area where a phone connected to a tower, but it does not always show the exact spot where you stood.
A defense attorney can also question how the expert reached a conclusion. An expert may interpret unclear data in a way that fits the prosecution’s theory while overlooking other explanations.
Challenging forensic experts in court
An attorney with forensic science training can ask detailed questions about testing methods and their limits. Missouri law requires expert testimony in criminal cases to rely on enough facts or data and reliable methods that the expert applies reliably. Those rules give the defense a basis to challenge weak expert opinions.
During cross-examination, an attorney can expose gaps between what the testing established and what the expert claims it proves. In some cases, those flaws can also support a request to keep unreliable evidence out of court.
Making questionable science answer for itself
If forensic evidence matters in your case, your attorney can review the test results, lab methods and expert opinions to uncover flaws the prosecution may not address. That review can give you a stronger basis for challenging evidence that does not support the certainty the prosecution claims.