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The Combined DNA Index System (CODIS) is the United States national DNA database created and maintained by the Federal Bureau of Investigation. CODIS consists of three levels of information; Local DNA Index Systems (LDIS) where DNA profiles originate, State DNA Index Systems (SDIS) which allows for laboratories within states to share information, and the National DNA Index System (NDIS) which allows states to compare DNA information with one another.
The CODIS software contains multiple different databases depending on the type of information being searched against. Examples of these databases include, missing persons, convicted offenders, and forensic samples collected from crime scenes. Each state, and the federal system, has different laws for collection, upload, and analysis of information contained within their database. However, for privacy reasons, the CODIS database does not contain any personal identifying information, such as the name associated with the DNA profile. The uploading agency is notified of any hits to their samples and are tasked with the dissemination of personal information pursuant to their laws.
The creation of a national DNA database within the US was first mention by the Technical Working Group on DNA Analysis Methods (TWGDAM) in 1989. In 1990, the FBI began a pilot DNA databasing program with 14 state and local laboratories. In 1994, Congress passed the DNA Identification Act which authorized the FBI to create a national DNA database of convicted offenders as well as separate databases for missing persons and forensic samples collected from crime scenes. The Act also required that laboratories participating in the CODIS program maintain accreditation from an independent nonprofit organization that is actively involved in the forensic fields and that scientists processing DNA samples for submission into CODIS maintain proficiency and are routinely tested to ensure the quality of the profiles being uploaded into the database. The national level of CODIS (NDIS) was implemented in October 1998. Today, all 50 states, the District of Columbia, federal law enforcement, the Army Laboratory, and Puerto Rico participate in national sharing of DNA profiles.
The bulk of identifications using CODIS rely on short tandem repeats (STRs) that are scattered throughout the human genome and on statistics that are used to calculate the rarity of that specific profile in the population. STRs are a type of copy-number variation and comprise a sequence of nucleotide base pairs that is repeated over and over again. At each location tested during DNA analysis, also known as a locus (plural loci), a person has two sets of repeats, one from the father and one from the mother. Each set is measured and the number of repeat copies is recorded. If both strands, inherited from the parents, contain the same number of repeats at that locus the person is said to be homozygous at that locus. If the repeat numbers differ they are said to be heterozygous. Every possible difference at a locus is an allele. This repeat determination is performed across a number of loci and the repeat values is the DNA profile that is uploaded to CODIS. As of January 1, 2017, requirements for upload to national level for known offender profiles is 20 loci.
Alternatively, CODIS allows for the upload of mitochondrial DNA (mtDNA) information into the missing persons indexes. Since mtDNA is passed down from mother to offspring it can be used to link remains to still living relatives who have the same mtDNA.
Prior to January 1, 2017, the national level of CODIS required that known offender profiles have a set of 13 loci called the "CODIS core". Since then, the requirement has expanded to include seven additional loci. Partial profiles are also allowed in CODIS in separate indexes and are common in crime scene samples that are degraded or are mixtures of multiple individuals. Upload of these profiles to the national level of CODIS requires at least eight of the core loci to be present as well as a profile rarity of 1 in 10 million (calculated using population statistics).
While some locus have a common name they are known by, such as CSF1PO, new loci follow a common naming scheme for uniformity. These loci are named D + the chromosome the locus is on + S + the location on that chromosome that is being tested. For example, D3S1358 is on the third chromosome at location 1358. The CODIS core are listed below; loci with asterisks are the "new" core and were added to the list in January 2017.
CODIS is an index of pointers to assist US public crime laboratories to compare and exchange DNA profiles. A record in the CODIS database, known as a CODIS DNA profile, consists of an individual's DNA profile, together with the sample's identifier and an identifier of the laboratory responsible for the profile. CODIS is not a criminal history database, like the National Crime Information Center (NCIC), and does not contain any personal identity information, such as names, dates of birth, and social security numbers.
Originally, CODIS consisted of the Convicted Offender Index and the Forensic Index, but in recent years, the Arrestee Index, the Missing or Unidentified Persons Index, and the Missing Persons Reference Index have been added. The Convicted Offender Index contains profiles of individuals convicted of crimes. State law governs which specific crimes are eligible for CODIS. (All 50 states have passed DNA legislation authorizing the collection of DNA profiles from convicted offenders for submission to CODIS.) The Forensic Index contains profiles developed from biological material found at crime-scenes.
CODIS has a matching algorithm that searches the various indexes against one another according to strict rules that protect personal privacy. In solving rapes and homicides, for example, CODIS searches the Forensic Index against itself and against the Offender Index. A Forensic to Forensic match provides an investigative lead that connects two or more previously unlinked cases. A Forensic to Offender match actually provides a suspect for an otherwise unsolved case. It is important to note that the CODIS matching algorithm only produces a list of candidate matches. Each candidate match is confirmed or refuted by a Qualified DNA Analyst. (To become Qualified, a DNA Analyst must meet specific education and experience requirements and undergo semi-annual proficiency tests administered by a third party.)
CODIS databases exist at the local, state, and national levels. This tiered architecture allows crime laboratories to control their own data—each laboratory decides which profiles it will share with the rest of the country. As of 2006, approximately 180 laboratories in all 50 states participate in CODIS. At the national level, the National DNA Index System, or NDIS, is operated by the FBI at an undisclosed location.
The National DNA Index (NDIS) contains over 12,010,904 offender profiles, 2,157,394 arrestee profiles and 663,191 forensic profiles as of October 2015. Ultimately, the success of the CODIS program will be measured by the crimes it helps to solve. CODIS’ primary metric, the “Investigation Aided,” tracks the number of criminal investigations where CODIS has added value to the investigative process. As of October 2015, CODIS has produced over 300,050 hits assisting in more than 285,447 investigations.
The CODIS database originally was primarily used to collect DNA of convicted sex offenders. Over time, this has expanded. Currently all fifty states have mandatory DNA collection from certain felony offenses such as sexual assault and homicide. Other states have gone further in collecting DNA samples from juveniles and all suspects arrested. In California, as a result of Proposition 69 in 2004, all suspects arrested for a felony, as well as some individuals convicted of misdemeanors, had their DNA collected starting in 2009. In addition to this, all members of the US Armed Services who are convicted at a Special court martial and above are ordered to provide DNA samples, even if their crime has no civilian equivalent (for example adultery).
Currently, the ACLU is concerned with the increased use of collecting DNA from arrested suspects rather than DNA testing for convicted felons. Along with the ACLU, civil libertarians oppose the use of a DNA database for privacy concerns as well as possible institutionalized discrimination policies in collection.
In forensics television series such as CSI, NCIS, Bones, Numb3rs, Criminal Minds, Law & Order: Special Victims Unit, Rizzoli & Isles and Dexter, the investigators often match DNA with the CODIS database. These media representations have had a considerable effect on how members of the public, but also professionals within the criminal justice system, and even prisoners, view the utility of DNA databases.