Combined DNA Index System

CODIS stands for Combined DNA Index System. It is the core of the national DNA database, established and funded by the Federal Bureau of Investigation (FBI), and developed specifically to enable public forensic DNA laboratories to create searchable DNA databases of authorized DNA profiles. The CODIS software permits laboratories throughout the country to share and compare DNA data. In addition, it provides a central database of the DNA profiles from all user laboratories. A weekly search is conducted of the DNA profiles in this national database, known as the National DNA Index System (NDIS) , and resulting matches are automatically returned by the software to the laboratory that originally submitted the DNA profile.

The term "CODIS" is often misused by law-enforcement officers, prosecutors and even practitioners of the forensic sciences when they intend to refer to a "DNA database." The index system has three levels of operation. The term "DNA database" is sometimes used without specific reference to the level, which may lead to misunderstandings. For example, some categories of profiles are allowed in a State's database but not in the National database. The term "CODIS lab" is also misused in reference to a state laboratory that does the analysis of convicted offender samples. That is a misnomer since CODIS also contain other profiles such as forensic profiles.

Basics of How CODIS Works

CODIS uses two indexes to generate investigative leads in crimes for which biological evidence is recovered from a crime scene. The convicted offender index contains DNA profiles of individuals convicted of certain crimes ranging from certain misdemeanors to sexual assault and murder. Each State has different "qualifying offenses" for which persons convicted of them must submit a biological sample for inclusion in the DNA database. The forensic index contains DNA profiles obtained from crime scene evidence, such as semen, saliva, or blood. CODIS uses computer software to automatically search across these indexes for a potential match.

A match made between profiles in the forensic index can link crime scenes to each other, possibly identifying serial offenders. Based on these "forensic hits," police in multiple jurisdictions or States can coordinate their respective investigations and share leads they have developed independent of each other. Matches made between the forensic and convicted offender indexes can provide investigators with the identity of a suspect(s). It is important to note that if an "offender hit" is obtained, that information typically is used as probable cause to obtain a new DNA sample from that suspect so the match can be confirmed by the crime laboratory before an arrest is made.