How Dna is used as Evidence in Criminal Trials

Due to remarkable advancements in DNA technology during the 1990s, it is now possible to more closely identify suspects in criminal cases. DNA analysis has become the best way to eliminate suspects, therefore making it easier to pinpoint the perpetrator of a crime. If the DNA profiles don’t match up, you have eliminated a suspect, and if they do you most likely have found the killer, rapist, or other type of crime suspect.

Cold cases

With this advancement in DNA technology, old cases that were never solved called “cold case files” have opened up a proliferation of detectives and DNA forensics specialists bringing these cases to trial. DNA evidence becomes the conclusive evidence in solving these old crimes where there was often a suspect but no clear-cut evidence for a trial or conviction, in which case, district attorneys would not even try the case.


Today DNA samples from incarcerated individuals and suspects are codified in a unique database system (CODIS) set up by the FBI that makes it easier for forensics specialists to identify a potential suspect. This Combined DNA Index System (CODIS) is coordinated with the National DNA Index System (NDIS) and the Criminal Justice Information Service-Wide Area Network (CJIS-WAN). [1]

Ethics in DNA evidence

Good DNA evidence in criminal trials depends on the integrity of handling the evidence by officials involved. The forensics laboratory used must be unbiased, offering fair, appropriate, accurate, and effective reporting and interpretation of results. [2]  [5] Therefore DNA forensics specialists must be highly trained and qualified for their profession.

Excellent DNA evidence becomes the most important factor in a criminal trial proceeding for conviction of the perpetrator of a crime. Once a detective has located DNA evidence to support the theory of a suspect, he can more easily get a confession from the suspect, which will also be used in the criminal trial. The more evidence available, the more likely there will be a conviction. Wrongful conviction is also reduced. [2]

DNA testing and analysis

DNA testing and analysis started out with RFLP (restriction fragment length polymorphism), which had the ability to analyze large biological samples such as the the size of a quarter. With technological advancements it is now possible to analyze fragments of evidence not visible to the naked eye and very degraded evidence. [3] [4]

New DNA technology

The new techniques used in DNA forensics are the PCR (polymerase chain reaction) analysis, which can analyze extremely small pieces of evidence or highly degraded evidence; the STR (short tandem repeat), which analyzes special regions on nuclear DNA codified by the the FBI as the 13-loci DNA and being able to identify a sample as high as one in one billion. [4]

The mitochondrial DNA (mtDNA) analyzes the mitochondrial area of a cell rather than the nucleus of the cell which can help to identify genetic material when it is impossible with PCR, STR, and RFLP such as in hair strands or old remains.[4]

Another type of DNA analysis is the Y-chromosome analysis that can help to identify genetic material where there are complex mixtures such as multiple male contributors in the case of rape. It can also locate a suspect through famial relations since the Y-chromosome is transmitted directly from the father to all sons. [4]


With these many new technologies available to forensics specialists, forensics laboratories, and law enforcement officials, very specialized DNA data regarding a crime is available and can substantiate criminal investigation and evidence in a criminal trial, thus affording relief to the families of the victims, and assuring a clear conviction without wrongful convictions that were the case when only fingerprint analysis and the testimony of witnesses was available. [2]

However there is controversy over the privacy of individuals regarding DNA databanking. Does it violate civil and human rights? Also there is evidence according to some sources that tampering and unusual political involvement can be the case regarding some trials and the collecting of evidence. [5]










Extra reading:

History of DNA technology:

A DNA forensics timeline: