DNA evidence from 48 sexual assault cases has been destroyed in what Aurora (Colo.) Police Chief Daniel Oates called a "tragic mistake."

"It was clearly a failure here on the part of the police department," Oates said at a news conference. "Occasionally in policing, organizations screw up and we certainly screwed up in this case. We are deeply regretful of that and we're doing the best we can to fix the matter."

The problem came to light when there was a DNA match made in a 2009 sex assault case, police said. When a detective went to pick up the evidence, he found out that it had been thrown out.

"The detective assigned to the case discovered that the remaining DNA evidence in APD custody, and all other evidence in the case, had been destroyed in error," the police department said in a news release. "The Department immediately began an investigation to determine the extent of the problem."

They found that evidence from 48 cases from 2009 had been destroyed. In 18 of the cases, the lead detective in each case had apparently recommended the destruction of the evidence, but there is supposed to be a review of each case before destruction, which did not occur, police said. In the other 30 cases, an injured officer assigned to "light duty" in the Property and Evidence Unit apparently mistakenly destroyed the evidence, police said.

"Well-intentioned people in the property and evidence section made a mistake here," Oates said. "We will do all that we should to fix this problem, including assigning blame where we have to."

Oates said that before the news conference he had gone to the home of a rape victim whose case will never be prosecuted because the evidence was destroyed.

"It was a difficult meeting. She was generous and gracious and understanding, a lot more understanding than I think I would have been," he said. "Obviously this is not a good day for our department."

The police chief said he has requested an expert panel to convene and review the situation.