The Combined DNA Index System (CODIS) is the national DNA database program maintained by the Federal Bureau of Investigation (FBI).
Created under the DNA Identification Act of 1994, CODIS provides criminal justice agencies across the United States with a centralized infrastructure to store, share, and cross-examine DNA profiles.
By connecting local, state, and national law enforcement laboratories, CODIS enables investigators to identify unknown suspects, link serial offenses across jurisdictions, and resolve missing persons cases.
The Three-Tier Architecture of CODIS
To balance local jurisdictional control with national search capabilities, CODIS operates across three interconnected operational levels:
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Local DNA Index System (LDIS): Operated by county or municipal crime laboratories. Laboratories initially analyze and enter DNA profiles generated from local crime scenes or arrests at this level.
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State DNA Index System (SDIS): Managed by a designated state agency (such as state police or department of justice). SDIS allows laboratories within the same state to compare profiles against statewide offender and forensic databases.
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National DNA Index System (NDIS): Maintained directly by the FBI. NDIS serves as the highest level of the system, enabling cross-jurisdictional profile searching across all 50 states, the District of Columbia, federal law enforcement, the U.S. Army Criminal Investigation Laboratory, and Puerto Rico.
Core Indexes Within CODIS
CODIS categorizes DNA profiles into distinct indexes based on the origin of the biological evidence, ensuring precise comparison and legal compliance:
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Database Index |
Profile Source & Operational Purpose |
| Forensic Index | Contains DNA profiles developed from biological crime scene evidence (e.g., blood, semen, saliva). |
| Convicted Offender Index | Stores profiles from individuals convicted of qualifying federal or state crimes. |
| Arrestee Index | Stores profiles from individuals arrested for qualifying crimes, depending on federal and state statutes. |
| Missing Persons Index | Holds DNA profiles from missing persons or reference samples provided by biological relatives. |
| Unidentified Human Remains Index | Contains DNA profiles developed from unidentified deceased individuals or recovered remains. |
How CODIS Works: Database Hits & Verification
CODIS automatically compares DNA profiles across its indexes to generate investigative leads:
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Offender Hit: Occurs when a crime scene DNA profile from the Forensic Index matches a profile in the Offender Index or Arrestee Index, identifying a potential suspect.
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Forensic Hit: Occurs when two or more crime scene profiles in the Forensic Index match each other, linking separate crime scenes to a single unknown perpetrator (e.g., serial offenses).
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Confirmatory Analysis: A database hit is treated as an investigative lead, not direct trial evidence. Before law enforcement acts, laboratory analysts conduct bench re-examinations to validate the match.
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Probable Cause & Reference Sample: Once verified, law enforcement uses the CODIS hit to obtain a search warrant for a direct, known biological reference sample (typically a cheek swab) from the suspect for court-admissible trial testing.
Privacy Protocols and System Security
Federal law strictly regulates the privacy and security of NDIS data to protect civil liberties:
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No Personally Identifiable Information (PII): CODIS does not store names, Social Security numbers, criminal histories, or medical records. Profiles consist solely of alphanumeric laboratory identification numbers, specimen IDs, and numeric Short Tandem Repeat (STR) allele values.
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Access Restrictions: Access to CODIS software and database networks is restricted exclusively to accredited criminal justice agencies and cleared forensic laboratory personnel.
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Accreditation Requirements: Under the DNA Identification Act of 1994, participating laboratories must maintain independent accreditation and adhere to strict quality assurance standards and audit compliance.
Frequently Asked Questions
What is CODIS and what does it stand for?
CODIS stands for the Combined DNA Index System. It is the automated DNA database system funded and maintained by the Federal Bureau of Investigation (FBI) that enables federal, state, and local crime laboratories to exchange and compare DNA profiles.
What is the difference between a CODIS offender hit and a forensic hit?
An offender hit occurs when a crime scene DNA profile matches a known individual in the Convicted Offender or Arrestee Index. A forensic hit occurs when two or more crime scene DNA profiles match each other, linking separate crime scenes without immediately revealing the suspect's identity.
Does CODIS store personal information like names and addresses?
No. CODIS does not contain personal identifying information such as names, birth dates, or Social Security numbers. It stores only the laboratory identification number, specimen ID number, analyst code, and the numerical STR DNA profile data.
How does CODIS help solve missing persons cases?
CODIS includes dedicated Missing Persons and Unidentified Human Remains Indexes. By comparing DNA profiles from recovered remains against reference samples donated by relatives of missing persons, the system can establish biological relationships and confirm identities.
Is a CODIS match enough to convict someone in court?
No. A CODIS match serves as an investigative lead. Forensic standards require the laboratory to re-verify the match and law enforcement to obtain a fresh, direct biological reference sample from the suspect for confirmation before presenting the DNA evidence in court.
