CODIS stands for Combined DNA Index System and is the national DNA database for the USA run by
the Federal Bureau of Investigations (FBI). It is a collective DNA database for three levels of
information in the USA: the Local DNA Index System (LDIS), the State DNA Index System (SDIS) and
National DNA Index System (NDIS). These DNA databases allow matches to be made from DNA
profiles from recently collected DNA samples, to DNA profiles previously stored in the databases.
DNA can be extracted for analysis from many different sources, such as blood, saliva, vaginal swabs,
semen or hair. To determine a DNA profile, scientists determine the number of Short Tandem
Repeats (STRs) corresponding to specific alleles for multiple different locations within our DNA. As of
January 2017, CODIS uses 20 different core loci, which allows for a very strong degree of certainty
that the match established will be correct.
CODIS
CODIS works by searching for unidentified profiles in various types of databases. If DNA found at a
crime scene has no obvious matches (i.e. to victim), the profile can be run against the database of
convicted offenders or arrestees from the particular state. Any match has to then undergo the
laboratory based procedures for confirming the match. If confirmed, identity of a person at the
crime scene would be established. Alternatively, the DNA profile could be searched against the state
database of DNA taken from crime scenes. As above, any match would need confirmation in the
laboratory, but once confirmed would be able to link two crime scenes together. Other databases
used for searches include indexes for unidentified human remains, missing persons, and relatives of
missing persons.
To confirm a match, the laboratories involved in analysing the two DNA profiles that appear to
match liaise in order to exchange and corroborate information. If there was no database match to a
suspect, but there was for two crime scenes, verification would allow documentation to be
produced to request a court order to collect reference DNA samples from suspects. Analysis of the
DNA profile, and comparison to the database and collected DNA profiles could then be presented as
evidence in court.
No personal identifiers of offenders, arrestees or detainees are stored on the databases. With the
profile itself, the only other information entered is an identifier for the laboratory submitting the
sample, an identification number for the sample and the laboratory staff associated with its analysis.
NDIS
The DNA Identification Act of 1994 allowed NDIS to be formed. The act specifies what types of
databases can be kept in NDIS as well as what is expected from participating laboratories relating to
quality assurance and privacy etc. It was first implemented in 1998 with all 50 states, Washington
D.C., the government, and Puerto Rico participating.
The types of DNA data that NDIS accept include PCR STRs, Y chromosome STRs (Y STRs), and
Mitochondrial DNA (mtDNA) analysis. Y STR and mtDNA data are only concerned with missing
person-related databases.
Unfortunately, the DNA of culprits at a crime scene is often destroyed during the process of trace evidence analysis, as forensic experts mostly use aggressive chemicals in order to discover fingerprints on exhibits. To analyse exhibits and keep the DNA in its original state a new innovative high-tech workstation was developed.
