What Does Using DNA for Police Investigations Entail?

Most police agencies routinely attempt to use DNA evidence in serious violent crimes. The National Research Council concluded that DNA is the only “forensic method [that] has been rigorously shown to have the capacity to consistently, and with a high degree of certainty, demonstrate a connection between evidence and a specific individual source” (Committee on Identifying the Needs of the Forensic Sciences Community, 2009: 7). Because of its effectiveness in identifying individuals (and suspects), police frequently attempt to collect DNA evidence in homicide and sexual assault cases. It has been less commonly used in property crime cases.

A multi-city experimental study by John Roman and colleagues suggests that using DNA evidence in property crime cases may also be an effective approach and can lead to a greater number of identified suspects than traditional investigation methods. The collection of DNA samples in burglaries was also found to be a cost-effective approach to dealing with property crime

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What is the Evidence on Using DNA in Police Investigations?

Using DNA in police investigations is listed under “What works?” on our Review of the Research Evidence. 

In the five sites (Orange County and Los Angeles, CA; Topeka, KS; Denver, CO; and Phoenix, AZ) in the Roman et al. study, rapid DNA testing led to higher rates of suspect identification and suspect arrest. In three of the five sites, the rate of suspect arrest in the DNA group versus the control group was more than twice as high. Identifying suspects alone, of course, does not indicate that crime rates will be affected, so more research is needed on the long-term impact of the increased use of DNA, but this research is very promising for police efforts to address crimes they are aware of. Additionally, DNA will likely only become more effective in identifying suspects as the size of national and local DNA databases continues to increase (as of April 2018, the National DNA Index contained over 13 million offender profiles).

Additionally since offenders identified by DNA had more than twice as many prior felony arrests as those identified by standard investigatory work, it is not unreasonable to argue that the increased use of DNA will help identify more high-rate offenders, which could have some beneficial impact on overall crime rates. In an era of low clearance rates for property crime (based on Uniform Crime Report data, just 13.1 percent of burglaries were cleared by arrest in 2016) and decreasing clearance rates for homicide, any changes that can improve the effectiveness of investigatory work should be welcomed by police.

The findings from a Campbell systematic review by Wilson and colleagues suggest that DNA testing can be a valuable tool for police investigators not only for establishing the guilt of identified suspects but also for identifying suspects whose DNA is already in law enforcement databases. The review found the strongest evidence of using DNA testing for property crimes and also found evidence of the value of DNA in more serious crimes, although these studies tended to be weaker methodologically.

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What Should Police Be Doing to Increase Use of DNA in Investigations?

The main implication of research in this area is that police agencies should continue to expand the use of DNA in investigations, particularly for crimes like burglary which have not traditionally been investigated by collecting DNA samples. The Roman et al. study did suggest that agencies can have issues implementing the expansion of DNA testing, in part because of limited resources for DNA analysis. While recognizing that agency budgets are currently stretched thin, efforts should be made to increase crime lab capabilities to reduce the outsourcing of DNA tests and backlogs in the analysis of evidence.

Interagency communication was found to be a very important aspect of successful implementation of expanded DNA testing. Police agencies must collaborate with local prosecutors and county and state crime labs to use DNA effectively.

Additionally, evidence technicians tended to be no better than patrol officers at obtaining usable samples for analysis. Because crime scene technicians tend to be more highly paid than patrol officers, this suggests potential long-term cost savings by training patrol officers on how to collect DNA samples.

Finally, blood and saliva samples tended to be better for collecting usable DNA samples than items the suspect held or touched, and it was best when officers or technicians collected entire items rather than just swabbing them at the scene.