Police departments across the nation are allowing rapists to get away with their crimes, while ignoring evidence that could solve these cases.

Congress heard testimony last week indicating that many big-city police departments are failing to test thousands of sets of evidence called "rape kits," which contain DNA collected from victims of sexual assault.

Each year, more than 100,000 people nationwide report being the victims of rape. Nearly all of them are asked to submit to invasive procedures to collect DNA samples from their bodies, samples that could provide the genetic fingerprints of their attacker's identity.

DNA can confirm a victim's account of being raped, identify a known assailant whose DNA is on computerized files with law enforcement authorities, or exonerate someone wrongly accused of a crime. It's one of the most valuable tools that police employ to investigate such cases.

But too often, these rape kits sit forgotten on shelves in police evidence lockers, untested by crime labs. The answers contained within them remain locked away.

The backlog of untested kits includes about 12,500 in Los Angeles, 10,000 in Detroit, 6,000 in San Diego, and 4,000 in Houston. (Philadelphia police, to their credit, say their lab tests every kit).

Explanations for this denial of justice range from police departments lacking money to conduct the tests, to overworked crime labs, to a failure to prioritize rape prosecutions. It's little wonder that only about 25 percent of rape cases nationally result in a perpetrator's being convicted.

Money shouldn't be a roadblock to solving these crimes. Congress passed a law in 2004 to provide grants to states for rape kit testing. But the law allows police departments to use the money for other DNA testing, not just rape kits. Human Rights Watch reported last March that the Los Angeles Police Department's backlog of untested rape kits occurred despite LAPD's receiving $8 million in grants for testing during the previous four years.

Bipartisan legislation now pending in Congress would require the federal government to collect data on the number of untested rape kits nationwide, and to prioritize the testing of this evidence. A pending House bill also would provide incentives to state and local law enforcement to eliminate the backlog of untested kits.

Lawmakers should move quickly to close this loophole in the five-year-old law. Too many victims of sexual assault are being denied answers and justice, when the solution may be sitting on a shelf.