Can DNA and Other Forensic Evidence Be Wrong?
Television crime shows have created a powerful impression about forensic evidence: a laboratory runs a test, a scientist announces the result, and the case is solved.
Real criminal cases are rarely that simple.
DNA, toxicology, fingerprints, firearms examinations, digital evidence, and other forensic testing can be extremely important. But the word “scientific” does not mean the evidence should automatically be accepted without examination.
Science is performed by people, using equipment, procedures, documentation, and judgment. Each part of that process deserves scrutiny.
DNA Evidence Is Powerful — but the Process Matters
Before a laboratory can produce a DNA result, someone must locate the potential evidence, collect it, package it, label it, preserve it, transport it, receive it at the laboratory, test it, interpret the results, and report the conclusions.
Problems anywhere in that process may affect how the evidence should be evaluated.
A defense lawyer may want to know who collected the sample, what precautions were taken to prevent contamination, how it was packaged, who handled it afterward, whether laboratory protocols were followed, and whether the underlying laboratory notes support the final report.
Those questions do not mean the forensic evidence is necessarily wrong. They mean it should be tested rather than simply accepted.
What Is the “Chain of Custody”?
Chain of custody refers generally to the history of the evidence from the time it is collected until it is tested or introduced in court.
Imagine that police collect an item at a crime scene. Who collected it? Where was it stored? Was it sealed? Who transported it? Who opened it? When did the laboratory receive it? Were there unexplained gaps?
Documentation matters because the prosecution must be able to establish that the evidence being presented is what the government says it is and has been handled appropriately.
Not every paperwork mistake will cause evidence to be excluded. But gaps, inconsistencies, contamination concerns, or failures to follow protocol may affect admissibility, reliability, or the weight a jury gives the evidence.
Why Can Two Experts Disagree?
Another misconception is that every qualified scientist looking at the same evidence will necessarily reach exactly the same conclusion. Sometimes they do. Sometimes they do not.
Testing methods can differ. Equipment can differ. The quality or quantity of a sample can matter. Interpretation can involve professional judgment. One expert may identify limitations that another expert did not emphasize.
That is one reason an independent expert can be valuable in the right criminal case. The defense does not necessarily have to accept the government’s expert as the final word.
The Report Is Only the Beginning
When forensic evidence is reviewed for the defense, the important questions include methodology, alternative explanations, documentation, chain of custody, and whether an independent expert would reach the same conclusion.
The answers can sometimes change how the entire case is viewed.
Scientific Evidence Should Be Examined, Not Feared
If the government says it has DNA, toxicology results, firearm evidence, computer evidence, or some other scientific proof, do not assume that the case is automatically over.
The right question is not simply, “Does the prosecution have forensic evidence?” The better question is: “How reliable is that evidence, and what does it actually prove?”
Need Help Evaluating Evidence in an Alabama Criminal Case?
Michael P. Hanle is a partner at Jaffe, Hanle, Whisonant & Knight, P.C. His practice includes criminal defense in Alabama state and federal courts.
This article is provided for general informational purposes only and is not legal advice. Every criminal case is different, and past results do not guarantee a particular outcome.
For more information, contact an experienced Birmingham criminal defense attorney at Jaffe, Hanle, Whisonant & Knight, P.C. for a free consultation.
We proudly serve clients in Birmingham and all throughout Alabama.
Jaffe, Hanle, Whisonant & Knight, P.C.
2320 Arlington Ave S, Suite 100, Birmingham, AL 35205
(205) 930-9800