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CODIS: Where will it take us in the future?

Updated on October 3, 2015

Combined DNA Index System

The Combined DNA Index System (CODIS) is the FBI-funded computer system that solves crimes by searching DNA profiles developed by federal, state, and local crime laboratories.

CODIS operates local, State, and national databases of DNA profiles from convicted offenders, unsolved crime scene evidence, and missing persons. Every State in the Nation has a statutory provision for the establishment of a DNA database that allows for the collection of DNA profiles from offenders convicted of particular crimes. CODIS software enables State, local and national law enforcement crime laboratories to compare DNA profiles electronically, thereby linking serial crimes to each other and identifying suspects by matching DNA profiles from crime scenes with profiles from convicted offenders. The success of CODIS is demonstrated by the thousands of matches that have linked serial cases to each other and cases that have been solved by matching crime scene evidence to known convicted offenders.

The missing person's index consists of the unidentified person's index and the reference index. The unidentified person's index contains DNA profiles from recovered remains, such as bone, teeth, or hair. The reference index contains DNA profiles from related individuals of missing persons so that they can be periodically compared to the unidentified persons index. All samples for this index are typed using mtDNA and STR DNA analysis (if possible) to maximize the power of advancing technology.

CODIS was an outgrowth of the Technical Working Group on DNA Analysis Methods (TWGDAM) which developed guidelines for standards of practice in U.S. and Canadian crime laboratories as they began DNA testing in the late 1980s.

TWGDAM was sponsored by the FBI Laboratory which hosted several scientific meetings a year at Quantico, VA, to accelerate development of laboratory guidelines and peer-reviewed papers to support forensic DNA testing which was, to some, an unproven forensic tool. TWGDAM completed a white paper in October 1989 which provided conceptual and operational concepts for a Combined DNA Index System to share DNA profiles among crime laboratories similarly to automated fingerprint matching which had become commonplace in law enforcement during the 1980s.

In late 1990, the FBI Laboratory began a pilot project with six state and local crime laboratories to develop software to support each lab's DNA testing and allow sharing of DNA profiles with other crime laboratories.

The DNA Identification Act of 1994 formally authorized the FBI to operate CODIS and set national standards for forensic DNA testing. TWGDAM guidelines served as interim standards until recommendations were provided by a DNA Advisory Board required under the Act.

The word "Index" in the CODIS name is not arbitrary. CODIS was designed to be a system of pointers to help public US crime laboratories compare and exchange DNA profiles. CODIS is not a criminal history database like the National Crime Information Center (NCIC). A record in the CODIS database, known as a CODIS profile, consists of a specimen identifier, an identifier for the laboratory responsible for the profile, and the results of the DNA analysis (known as the DNA profile). Other than the DNA profile, CODIS does not contain any personal identity information -- the system does not store names, dates of birth, social security numbers, etc.

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.

In its original form, CODIS consisted of two indexes: the Convicted Offender Index and the Forensic Index. 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 authorization 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. In the past several years, CODIS has added several other indexes, including: an Arrestee Index, a Missing or Unidentified Persons Index, and a Missing Persons Reference Index.

CODIS has a matching algorithm that searches the various indexes against one another according to strict rules that protect personal privacy. For solving rapes and homicides, 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 3rd 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. The national level, the National DNA Index System, or NDIS, is operated by the FBI at an undisclosed location.

CODIS is implemented as a distributed database with three hierarchical levels (or tiers)—local, State, and national. All three levels contain forensic and convicted offender indexes and a population file (used to generate statistics). The hierarchical design provides State and local laboratories with the flexibility to configure CODIS to meet their specific legislative and technical needs.

A description of the three CODIS tiers follows:

  • Local. Typically, the Local DNA Index System (LDIS) installed at crime laboratories is operated by police departments or sheriffs’ offices. DNA profiles originated at the local level can be transmitted to the State and national levels.
  • State. Each State has a designated laboratory that operates the State DNA Index System (SDIS). SDIS allows local laboratories within that State to compare DNA profiles. SDIS also is the communication path between the local and national tiers. SDIS is typically operated by the agency responsible for implementing and monitoring compliance with the State’s convicted offender statute.
  • National. The National DNA Index System (NDIS) is the highest level of the CODIS hierarchy and enables qualified State laboratories that are actively participating in CODIS to compare DNA profiles. NDIS is maintained by the FBI under the authority of the DNA Identification Act of 1994.

The more data contained in the forensic and offender indexes of CODIS, the more powerful a tool it becomes for law enforcement, especially in its application to unsolved case investigation. However, because many jurisdictions are in the process of developing and populating their DNA databases, convicted offender and forensic casework backlogs have been created over time and continue to grow for several reasons. First, as States recognize the crime-solving potential of DNA databases, they continue to expand the scope of their convicted offender legislation, which increases the number of the offender index, contains DNA profiles of individuals convicted of certain crimes. The forensic index contains DNA profiles obtained from crime scene evidence. Samples to be collected and analyzed by the DNA laboratory. As a result, more than 1 million uncollected convicted offender DNA profiles are “owed” to the system.

An equally important but more difficult problem to quantify is that of unprocessed casework that contains biological evidence. This casework backlog may include nonsuspect or unsolved cases that could be analyzed and solved as a result of advancements in DNA technology.

As of November 2005, 124,200 forensic profiles and 2.8 million offender profiles have been accumulated, making it the second largest DNA databank in the world behind the United Kingdom's National DNA Database. As of the same date, CODIS has produced over 27,700 matches to requests, assisting in more than 29,600 investigations.

The growing public approval of DNA databases has seen the creation and expansion of many states' own DNA databanks in future. California currently maintains the third largest DNA databank in the world (naturally, as CODIS contains all states' databank information). Political measures such as California Proposition 69 (2004), which increased the scope of the databank, have already met with a significant increase in numbers of investigations aided.

Practical Considerations

A broad range of considerations must be made long before any DNA testing is actually attempted in older, unsolved cases. These include:

  • Legal considerations, such as the application or expiration of statutes of limitation.
  • Technological considerations, such as the nature and condition of the evidence as originally collected, stored, and in some instances, subjected to other forensic tests.
  • Practical considerations, such as the availability of witnesses in the event DNA testing would identify a suspect and lead to an arrest and a trial.
  • Resource issues, such as the time and money available for investigation and forensic analysis.

The nature and scope of these issues require that any approach to reexamining old cases for potential DNA evidence is collaborative, whether by an individual investigator or by a specialized unit developed specifically for cold case review. Local prosecutors can provide valuable insight into legal issues that might prevent or help a future prosecution. Victim/witness units or advocates can provide valuable assistance with locating, educating, and encouraging witnesses. Consultation with representatives from the crime laboratory is critical to ensuring that potential DNA evidence can be successfully analyzed in the future.

In order to decrease the number of irrelevant matches at NDIS in the future, the Convicted Offender Index requires all 13 CODIS STRs to be present for a profile upload. Forensic profiles only require 10 of the STRs to be present for an upload.

The CODIS database originally was only used to collect DNA of convicted sex offenders. Over time, this has expanded. Currently all fifty states have mandatory DNA collection from sex offenders and nearly 40 states from all convicted felons. 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, within five years all suspects arrested for a felony, as well as some individuals convicted of misdemeanors, will mandatorially have their DNA collected.

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.


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