Trace DNA, or touch DNA, is tiny amounts of genetic material left on an object after brief contact. Just a few skin cells can create a DNA profile. This evidence can connect someone to a crime scene, but it can also lead to mistakes. In Maryland, appeals courts often see cases where trace DNA evidence is questioned due to errors at trial or unreliable expert opinions.
Common problems with trace DNA evidence
Maryland law has strict rules for using DNA evidence, but touch DNA has risks that appeals courts may examine:
- Secondary transfer: DNA can move from one person to an object and then to another person. This can create false links to a crime scene. Concerns about secondary transfer, where DNA moves indirectly between people and objects, are well-documented in forensic science and can raise doubts about the meaning of trace DNA evidence.
- Mixed samples: Labs often test DNA from multiple people in one sample. The interpretation of small or mixed DNA samples is inherently complex and requires sophisticated statistical analysis, and the reliability of these interpretations is often a critical issue in legal challenges. This can go against standards set by the Maryland State Police Forensic Sciences Division.
- Software reliability: Maryland’s appeals court recently supported the use of probabilistic genotyping software in a Baltimore murder case. However, it stressed that experts must clearly explain the software’s limits.
If the defense shows that unreliable DNA evidence likely affected the trial’s outcome, these issues can support an appeal.
Raising trace DNA issues on appeal
Under Maryland’s Criminal Procedure § 8-201, you can request DNA testing after a conviction. Separately, under Md. Crim. Proc. § 8-301, a person may be able to file a petition for a Writ of Actual Innocence based on ‘newly discovered evidence,’ which could include new scientific findings or standards that undermine the evidence used at trial. During an appeal, you might ask:
- Did the DNA collection and testing follow proper chain-of-custody rules?
- Was the DNA evidence admitted without a strong scientific basis?
- Did your trial lawyer fail to consult a qualified DNA expert or question statistical results?
If judges find that flawed DNA evidence helped lead to a conviction, they may grant a new trial or send the case back for review.
Why this matters
Trace DNA evidence can seem convincing, but Maryland courts know it has limits. If trace DNA was a major factor in your conviction, carefully reviewing lab methods, expert testimony, and transfer risks could change the outcome. This could mean the difference between a final ruling and a new opportunity for justice.