Four reasons forensic evidence can be unreliable in a criminal case

Forensic evidence can be unreliable due to professional errors or misconduct; mischaracterization at trial; and the use of unvalidated techniques.

Compared to other forms of evidence that may be used to support criminal charges, forensic evidence is often regarded as highly objective and reliable. This evidence may be especially influential in cases where people face serious charges, such as violent crime or sex offense charges. Unfortunately, this does not mean that wrongful convictions involving flawed forensic evidence never occur.

Here in Florida, 15 out of 68 known wrongful convictions - or over one in five cases - have been at least partly attributed to issues with forensic evidence, according to the National Registry of Exonerations. As a result, it is critical for the potential issues with this type of evidence to be closely considered during any criminal case.

1. Unvalidated techniques

Many people assume that all forensic techniques have been proven valid through extensive scientific research and testing. However, for many widely used techniques, an objective review process and clear evidence of effectiveness are often lacking. For example, according to the Los Angeles Times, a report from the President's Council of Advisors on Science and Technology that was released in 2016 concluded that the following forms of evidence lack solid scientific support:

· Bite mark comparisons

· Firearm and tool mark analysis

· Shoe print comparisons

· Analysis of "mixed" DNA samples

Consequently, the report recommends that these forms of evidence be withheld from trial or introduced only with an appropriate warning about their reliability.

2. Overstatement of accuracy

Unfortunately, jurors are often asked to consider forensic evidence without fully understanding its limitations. When testifying during trial, analysts may neglect to mention the shortcomings of a forensic method, or they may even overstate its reliability. For example, an investigation of 268 cases involving testimony from FBI analysts found that the analysts mischaracterized or exaggerated the efficacy of hair microscopy in 96 percent of the reviewed cases.

3. Errors in analysis

Even when a case hinges on valid forensic techniques, there is a potential for harmful errors. In one bizarre case, an innocent man in Orlando was arrested for drug possession after a police officer mistook donut glaze in the man's vehicle for amphetamine. According to The Orlando Sentinel, the officer, who was never trained to use a drug test kit, performed one test with the wrong kit and two tests that yielded false results due to errors. Fortunately, charges against the man were dropped when a state crime lab determined that the substance was not a narcotic.

Sadly, the outcome for innocent individuals may be markedly different when similar errors occur in a laboratory setting. Due to factors such as inadequate training, short staffing or limited oversight, it is not unheard of for analysts to mix up specimens, accidentally contaminate samples or improperly administer tests.

4. Misconduct by authorities

Less frequently, deliberate misconduct on the part of forensic analysts may lead to wrongful convictions. Some analysts may see themselves as part of the prosecutorial team or cut corners to appear more proficient at their jobs. These individuals may report results without conducting any tests, fabricate false results or suppress evidence that could help an accused individual's case.

In light of these various potential issues, anyone who has been charged with a criminal offense based on forensic evidence should seek legal advice. An attorney may be able to help a person develop a strategy for challenging the charges, based on known problems with forensic evidence or other relevant issues.