Crime: How the Combined DNA Index System (CODIS) works in high-profile and cold cases

Source: FBI

Q: How does CODIS handle high-profile cases such as serial killer Ted Bundy’s DNA, which was recently tested so it could be entered into the system?

Hares: At the national level, we don’t know about the evidentiary profiles entered into CODIS by the states. While the DNA profiles use specimen identification numbers, such identification numbers do not contain personal identifiers that would allow us to pick out a particular profile from the database as belonging to a specific person. For example, even if a state informs us that they have uploaded a high-profile sample like Bundy’s, at the national level we don’t know which profile is his because there is no personal identifying information attached to it. The system is designed to be completely anonymous to protect personal privacy—until a match occurs and the requesting state can learn the offender’s identity. But this raises the importance of analyzing the DNA from such serial offenders, even if the offender is deceased, so that the DNA profile can be searched against those unsolved cold cases.

Q: Is CODIS effective in cold cases?

Hares: Absolutely—that demonstrates the power of CODIS. If you are able to obtain a DNA profile from a case that remained unsolved from years ago and place that profile into the system, there is a good chance you may get a hit because the offender may have committed other crimes and been required to provide a DNA sample.

Q: How does technology help CODIS?

Hares: It’s important that all authorized profiles are entered into CODIS in a timely manner. The sooner profiles are entered into the system, the sooner CODIS can help solve crimes. Sometimes, when DNA database programs with limited resources expand to add categories of persons required to provide DNA samples, backlogs in samples to be analyzed and entered into CODIS may develop. The FBI encountered such a situation when the law expanded DNA sample collection to federal arrestees and detainees. But thanks to a National Institute of Justice grant and the use of robotics and expert systems, we eliminated a backlog of more than 300,000 offender profiles in a matter of months. That achievement was recognized in a recent audit by the Department of Justice Office of Inspector General.

Q: As technology is integrated into DNA processes, what can we expect from CODIS in the future?

Hares: We have seen that as the number of DNA profiles in CODIS increases, the system helps solve more crimes. Now we are aiding more investigations in a single year than we did in the first five years of the system’s existence. It’s all due to the size of the database—increasing the number of authorized profiles for the state and national databases results in additional DNA profiles that could be linked to unsolved crimes. Since the creation of CODIS, we have aided over 152,000 investigations—that’s an impressive number of crimes that may not have been solved by any other method. The statistics speak for themselves. As we continue to add more profiles, the potential to solve more crimes—and also to rule out suspects who are innocent—continues to increase.

Making a Match

To determine an individual’s DNA profile, CODIS uses identification markers called short tandem repeats, or STRs.

“We look at 13 different chromosomal locations or markers,” said Douglas Hares, NDIS custodian. “It’s the combination of those different locations that makes the DNA profile a powerful identifier.” For an evidentiary or forensic unknown profile to be searched at the national level, it must have data for at least 10 of these markers. Known offenders in the system must have data for all 13 markers.

“You need that amount of information to be confident about matches,” Hares said. “It’s like a license plate. If you only search three letters or numbers of a license plate, you will get a lot of false matches. We require the threshold to be much higher to prevent those false matches.”

CODIS markers are selected solely for their identification value and are not associated with any type of physical trait or medical condition, Hares explained, adding that in the future, as the system grows, “we are looking at expanding our 13 core markers.”