The purpose of DNA databases is to solve crimes that would otherwise be unsolvable. A common method of measuring the effectiveness of CODIS or any
The capabilities of forensic DNA testing have generated new legal issues for prosecutors. The sensitivity of the polymerase chain reaction enables DNA profiles to be obtained from previously intractable evidence. Furthermore, the existence of DNA databases now permits matches between perpetrators of crimes spanning jurisdictions and 'cold hits' on unsolved crimes many years after they occurred.
Many states have statutes of limitations meaning that after a certain period of time a crime cannot be prosecuted. If DNA evidence exists from a crime scene yet no suspect has been located to be charged with the crime, a 'John Doe' warrant may be issued based solely on the assailant's genetic code. In September 1999 Norman Gahn, Assistant District Attorney from Milwaukee County, Wisconsin, filed the first warrant for the arrest of 'John Doe', an unknown male who could be identified by his 13 locus STR profile. This approach has been successful in stopping the ticking clock of a crime's statute of limitations making it possible to prosecute the crime when the assailant is identified through a DNA database cold hit in the future. Several of these 'John Doe's' have been subsequently identified with DNA database cold hits and successfully prosecuted for the crimes they committed.
Wisconsin law governing the statute of limitations was amended in September 2001 to provide for the use of DNA profiles from individuals unknown to the prosecution at the time the warrant for arrest is issued. The new legislation creates an exception to the time limits for prosecuting sexual assault crimes if the State has DNA evidence related to the crime. John Doe warrants have also been issued in other states.
Silent Witness, Volume 7, Number 1, 2002, American Prosecutors Research
Institute (see www.ndaa-apri.org)
other DNA database is in what is referred to as a 'hit.' A hit is a confirmed match between two or more DNA profiles discovered by the database search. Within CODIS, hits may occur at a local (LDIS), state (SDIS), or national (NDIS) level.
Hits fall into two different categories. A forensic hit occurs when two or more forensic casework samples are linked at LDIS, SDIS, or NDIS. These types of hits are sometimes called case-to-case hits and are especially important to solving serial crimes. An offender hit occurs when one or more forensic samples are linked to a convicted offender sample. These types of hits are sometimes referred to as case-to-offender hits. Either type of hit contributes to the bottomline performance metric of a DNA database - the number of criminal investigations aided. In the first five years of operation (1998-2003), the CODIS system aided more than 15 000 investigations in the United States.
DNA databases work because most criminals are repeat offenders (McEwen and Reilly 1994, Langan and Levin 2002). If their DNA profile can be entered into the system early in their criminal career, then they can be identified when future crimes are committed. Serial crimes can also be linked effectively with a computer database. Ultimately, the value of the DNA database is in its ability to apprehend criminals that are not direct suspects in a case and to prevent further victims from crimes committed by those individuals.
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