What is CODIS? A Forensics Professional’s Guide

The Combined DNA Index System, commonly known as CODIS, is a tool used by law enforcement agencies to aid in solving crimes. Developed and maintained by the FBI, it is one of the largest DNA databases in the world, containing over 14 million offender profiles and over four million arrestee profiles, along with profiles from crime scenes, missing persons, and unidentified human remains.

CODIS went live in 1994, bringing together fragmented state and local DNA data into one master database. It began with DNA profiles from convicted offenders and forensic samples but has widened over time, particularly as state and federal laws have expanded the scope of DNA sample collection to include arrestees.

Advances in DNA analysis techniques have further improved the system’s effectiveness. But while today’s version of CODIS is an extremely powerful tool in forensics and law enforcement, it’s not a catchall solution.

To learn more, read on.

Meet the Expert: Monica Rockswold

Monica Rockswold is an international forensic biology trainer at the Global Forensic and Justice Center (GFJC) at Florida International University (FIU). She earned her bachelor of science in forensic science from the University of Central Florida. Rockswold has over 17 years of experience in forensics, with 14 years of those years spent in an accredited crime laboratory working in the disciplines of seized drugs, gunshot residue, firearms, and biology. She has, to date, trained individuals from five countries, nine crime laboratories, and two universities.

Biggest Misconceptions Around CODIS

“The biggest misconception is that people think CODIS itself will solve crimes,” Rockswold says. “But it doesn’t solve crimes. It just links information.”

CODIS’s primary function is to facilitate connections between DNA evidence collected from different crime scenes, suspects, and victims. It can link cases with people, cases with cases, and even help identify missing persons. But it’s a very controlled database, and the only profiles that get added are ones that link, with certainty, to a particular case. Submissions to CODIS need to be approved by an administrator.

To be clear: forensics professionals aren’t searching for someone up in CODIS the way the average person searches something up on the internet. The data in CODIS is de-identified, such that all the searcher can see is the DNA sample—the alleles themselves—and whether there are potential matches in the system. This prevents instances of bias from creeping in.

How Forensics Professionals Work with CODIS

Not every lab has access to CODIS. But if it does, forensics professionals will receive some specialized training in it before receiving their personal identification information, which allows them to log in securely to CODIS.

When adding information to CODIS, a forensics professional will add a unique ID for the case. There is a specific protocol for identifying information, and it’s based on where the lab is located, what the case number is, and what type of profile is being entered. The forensics professional will take their allele calls—the numbers they receive on an electropherogram—and add the DNA profile into CODIS. Once they’ve submitted those numbers, they will be asked, on a fresh screen, to enter them a second time as a failsafe to ensure the information has been entered correctly.

After submitting the DNA profile, a forensics professional will get back information about any potential matches to other profiles in the wider CODIS database. Then, as a trained analyst, it’s their job to go through and assess those potential matches to determine whether they are, indeed, matches. If they are, a CODIS administrator may be able to supply further information. Afterward, the forensics professional can write a report detailing their findings.

Strengths and Weaknesses of CODIS

CODIS has been around for decades now. It has enormous amounts of information for forensics professionals to draw upon. Files don’t get lost the way they might’ve in the paper era. And CODIS’s memory doesn’t fog the way a detective’s might. This tool gets stronger with age: not only working in the present moment but also helping catch serious offenders from other offenses and solving cold cases.

“The more information CODIS has, the better chance there is of linking information through it,” Rockswold says.

It’s not without its weaknesses. There’s a lot of data for CODIS to store, and an intricate web of oversight and security is required to maintain individuals’ privacy. Updates to kit chemistry, the number of areas tested, and forensics processes mean samples processed at present provide more information than ones processed years ago.

“Newer kits gather more information,” Rockswold says. “Before, we were looking at 13 areas, and now we’re looking at 20, at least. You can get more potential hits, but you also have to do more investigation to see whether that’s a true hit or not.”

Even when there’s a potential match in CODIS, there’s a prudent culture of caution and redundancy. For example, forensics professionals will ask for a fresh buccal swab to verify that the profile in CODIS matches the person it’s attached to. This highlights a recurring theme: CODIS as an investigative support tool, rather than the arbiter of truth and justice.

“We’re never going to solve a crime just because CODIS says we have a potential hit,” Rockswold says. “It’s a tool to create more possible leads, to narrow things down. And as an analyst, you will always go back and work your findings again.”

Today, CODIS is used in so many cases that it would be impossible for most forensics professionals to recount them all. But while Rockswold has seen many CODIS hits in her career, one stands out above the others.

“I had two individuals, where I knew who they were, and I got their profiles and added them to CODIS,” Rockswold says. “I got a stack of hits. My report from CODIS is usually about a page and a half long—this one was six pages long, and they were all real hits.”

It turned out that those two individuals had been involved in a string of as-yet-unsolved crimes, and Rockswold’s analysis was the first time that either of them had been successfully identified. Rockswold’s entry of their information into CODIS provided the critical missing link, bringing several cases to justice, and potentially preventing future crimes.

The Future of CODIS

The CODIS system will continue to expand in the future. However, while the FBI has begun combining other forms of biometric data—iris scans, facial features, fingerprints, and palm prints, for example—it’s unlikely to combine any of those with CODIS. The CODIS database is designed to be as unbiased as possible; extraneous identifying information could hamper that.

“I don’t think there’s any push to integrate CODIS with actual identity markers such as irises and fingerprints,” Rockswold says.

Advances in DNA testing are promising to make CODIS more effective for forensics professionals and law enforcement. Some law enforcement agencies are already working with rapid DNA technology, where they can take a cheek swab from an arrestee, run it through a specialized instrument, and get a DNA profile back within an hour and a half.

“It’s a very quick system compared to traditional DNA analysis,” Rockswold says.

Police departments don’t have the personnel to work with incomplete profiles, but if they’re able to get a complete profile from the swab, they can automatically upload it to CODIS and do some preliminary searches—for example, for violent offenses—and see if there are any preliminary hits. That can help inform whether someone should be released or detained longer.

“Within 24 hours, it will search the state level of the database, and they’ll know what to do with that individual,” Rockswold says. “That can help keep really dangerous people off the streets and shorten the time for catching criminals.”