Combined DNA Index System (CODIS), which was developed in 1990 and contains DNA profiles at the national, state, and local level. Similarly, the need to solve sexual assault crimes in Brazil led the Forensic DNA Research Institute of Federal District Civil Police to create a DNA database in 1998 containing evidence specifically collected in sexual assault cases. DNA matches in such databases not only aid in identifying the assailant where unknown to the victim, but also may help determine whether the assailant (known or unknown to the victim) is a serial rapist. These findings eventually may be made available for use in court. In some cases, the rape kit does not yield DNA evidence and the forensic scientist is unable to develop a DNA profile of the assailant. This may be because the assailant did not leave DNA behind, or too much time passed before the victim had a rape kit exam performed, or the rape kit evidence may have been improperly collected, stored or handled. Due to the backlog of sexual assault cases, forensic scientists have been challenged with the task of determining how to process the sexual assault kits effectively and within the statute of limitation on assaults. Damaged evidence is something that is common among rape kits because survivors of sexual assault typically desire to wash themselves as soon as possible following an attack. Prior to the exam, it is desired that patients avoid using the rest room, combing their hair, bathing, changing their clothes or cleaning up the scene of the assault. Most evidence needs to be collected within 72 hours to be viable, and patients are advised to either bring or wear the clothing they had on when attacked to the exam. Influence on sexual assault cases Rape kit evidence can aid the criminal rape investigation and the prosecution of a suspected assailant. It may also be used to exonerate the wrongly accused. The benefit of rape kit evidence depends in part on the character of the assault. Stranger cases In stranger sexual assault cases, the assailant is unknown to the victim. In such cases, rape kits may be instrumental in identifying the assailant through DNA profiling, which research suggests may help lead to an arrest. For example, a 2009 study examining sexual assault cases from two of 389 crime laboratories in the United States found that stranger-rape cases with forensic evidence were 24 times