Public crime laboratories across the country contribute samples to the national database that is maintained by the FBI. The CODIS software is provided by the FBI to public forensic laboratories at no cost. However, the cost of the computer hardware and all support software are the laboratory's responsibility. Upgrades and technical support of the software are also provided free to all laboratories.
CODIS generates investigative leads using two indexes: The Forensic Index and the Offender Index. The Forensic Index contains DNA profiles from crime scene evidence, and the Offender Index contains DNA profiles of individuals who have been convicted of various offenses defined by state and/or federal law.
Five years after launching the CODIS project, the Federal DNA Identification Act was enacted as part of the Violent Crime Control and Law Enforcement Act of 1995. It authorized the FBI to establish a national database, or National DNA Index System (NDIS), for law enforcement.
Since then, public laboratories have invested significant resources toward developing local and state DNA databases, which serve to populate NDIS.
The CODIS system operates on three levels:
The three-tiered system allows state and local agencies to operate their individual databases within the confines of state laws, which can vary from jurisdiction to jurisdiction.
When the CODIS software recognizes the same DNA profile in the Forensic or Offender Index, it identifies the two profiles as a match. These matches are commonly referred to as "hits."
After the CODIS software generates a hit, laboratory personnel may reanalyze samples to validate the match.
When a DNA profile in the Forensic Index matches another profile in the Forensic Index, crime scenes can be linked together. These hits enable investigators to identify serial offenders, coordinate investigations, and share leads across multiple jurisdictions.
When a profile in the Forensic Index matches a profile in the Offender Index, the hit may reveal the identity of the perpetrator or another person who was present at the crime scene. This type of hit is normally used as probable cause to get a new biological sample from the offender to confirm the hit and to compare with the crime scene evidence.
Such a match occurred during the investigation of the case study crime and enabled investigators to advance their case against a former person of interest.