CODIS: Combined DNA Index System

By Sarah Rackley
Edited by Dr. Maher Noureddine, forensic DNA expert

Note: Where State Crime Lab policies and procedures are referenced, I have cited to the most recent version that I have access to.

What it is:
CODIS (Combined DNA Index System) is the FBI’s program that allows forensic DNA laboratories to create and search databases of DNA profiles. The federal DNA Identification Act of 1994 authorized the FBI to create CODIS and set national standards for forensic DNA testing. CODIS became fully operational in 1998. CODIS databases exist at the local (LDIS), state (SDIS), and national levels (NDIS). This tiered architecture allows crime laboratories to control their own data, enabling each laboratory to decide which profiles it will share with the rest of the country (Source:,

How it is used:
CODIS contains an index of convicted offender and arrestee profiles. These profiles are developed from biological samples submitted when an individual is arrested for or convicted of statutorily specified crimes. (See Crime Lab procedures for CODIS and DNA Database Procedures.) Each state has different qualifying offenses, and there are requirements for entering the profiles into the local, state, or national database. (See G.S. 15A-266)

When biological evidence is collected from a crime scene or victim, a DNA profile of a suspect may be developed. This “forensic unknown profile” can be compared to profiles in the convicted offender and arrestee index. Regular searches are conducted of all DNA profiles in the National DNA Index System (NDIS) and resulting profile matches are automatically returned to laboratories that submitted them.

If there is a computer-identified “match” or “offender hit,” the Crime Lab initiates procedures to obtain a new DNA sample from the suspect and perform  DNA analysis in the lab to confirm the match. If you have a case where a CODIS hit was made, it is important to read Section 6 of the Crime Lab Procedures to ensure that the correct reviews and analysis has occurred.

Considerations if you have a CODIS cold hit case:

  • Is there a direct or reasonable correlation between the forensic sample that was collected from the scene and the crime itself? What are the chances that the sample belongs to a bystander, unrelated to the crime? This is especially important if the sample was developed as a “Touch DNA” sample. Using new technologies, minute amounts of genetic material can now be used to generate a profile that is suitable for CODIS.
  • How was the “forensic unknown profile” from the crime scene entered into CODIS? Consider possible sample mix up, contamination, and interpretation problems that could have occurred when the sample was entered. Who was the analyst who entered the sample? Some of the analysts who entered samples in the early 2000s are no longer employed by the State Crime Lab or were cited in the Swecker report, which raised concerns about the reliability of Crime Lab work.
  • How and why was the DNA sample collected from your client? Are there grounds to challenge that collection? If your client’s sample was in the database from a collection in NC, was the qualifying conviction or arrest pursuant to G.S. 15A-266.3?
  • Have you received the lab report from the Crime Lab’s analysis of the database “match?”
  • Finally, consider the standard questions you would ask regarding DNA analysis: How many loci match? What is the statistical significance of the “match”? (See this LA Times article.) How was that statistical significance calculated? (See this research on the probability of an erroneous attribution in “cold hit” cases) How did cognitive bias affect the analysis?

Motions practice:
A great resource for motions you may consider filing in CODIS cold hit cases is PocketExpert Consulting, LLC. This website has sample motions including the following challenges: when DNA has been taken from a client who has not committed a qualifying offense, the taking of DNA from a parolee, the statistical significance of the purported “cold hit,” the unreliability of a 9+ loci match, and CODIS vulnerabilities.

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