Evidence from more than 6,600 rape kits that went untested for years in Houston have turned up 850 hits in the FBI's nationwide database of DNA profiles, marking a major step in the city's $6 million effort to address the backlog, officials announced Monday.

Charges have been filed against 29 people, six of whom have been convicted, since the city launched an effort in 2013 to test 6,663 rape kits — some of which dated back nearly three decades. Testing was completed in the fall, and the results have now been uploaded to a database used by investigators nationwide to compare DNA profiles of possible suspects, Mayor Annise Parker said.

"This milestone is of special importance to rape survivors and their families and friends because it means their cases are receiving the attention they should have years ago," Parker said at a news conference, where she joined local law enforcement officials to announce the results.

Police are continuing to review the matches to see if charges can be filed in other cases. In the cases where prosecutors have won convictions, defendants have received sentences ranging from 2 to 45 years in prison. One case was dismissed after the victim decided not to pursue the case.

Rape kits include biological samples and physical evidence gathered from sexual assault victims that are later processed to see if they match a suspect's DNA. Testing results are uploaded to the FBI's Combined DNA Index System, or CODIS.

Harris County District Attorney Devon Anderson said there were some cases where suspects committed other crimes while rape kits that could have identified them sat untested.

"Now that the testing of these kits is complete, we know that it's up to us to finish the job and to seek justice for these victims. The ball is in our court and we will do our best to put the people who are responsible for these heinous crimes behind bars for as long as possible," she said.

Experts say Houston's backlog — and similar backlogs in other U.S. cities — are due in part to the high cost of testing which can run from $500 to $1,000 per kit, though advocates argue that the lack of testing signals that sex crimes haven't always been law enforcement priorities.

More than 12,000 kits went untested for years in Memphis, Tennessee, which is facing a lawsuit from rape victims as it tries to test the kits. In Detroit, prosecutors discovered more than 11,000 rape kits in an abandoned police warehouse in 2009, and Cleveland prosecutors have sent their entire 4,700-kit backlog for testing.

"This is not a Houston problem. It's not a Texas problem. It's a nationwide issue that built up over years and years," Parker said.

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