Diana Cunningham of Columbus, Ohio, was raped last June. What makes it even worse, she says, is that the man accused of assaulting her would probably have been behind bars -- if only authorities had processed a DNA sample from another case.
According to a recent Justice Department study, there are more than 540,000 cases, including 69,000 homicides, where DNA evidence -- which is often the difference in proving guilt or innocence -- is still sitting in police precincts or state laboratories, waiting to be tested.
Robert Patton, the man whom Cunningham says raped her, was charged in 2001 with kidnapping, and a mandatory DNA sample was collected at the time of his incarceration. (ABC News normally withholds the names of sexual assault victims, but Cunningham allowed her name to be used.)
But the sample sat on a shelf untested for three years. When it was finally examined, police made a stunning discovery. They say the DNA linked Patton to 37 rapes -- 13 of them committed while his sample languished.
Cunningham says she was one of the 13 victims.
"I am angry that they allowed this to happen," she said. "Had they done it a week before, I would not have been attacked."
Police say hundreds of rapes and homicides will be committed by repeat offenders who could have been brought to justice.
"We have a lot of cases out there that could be solved and aren't being solved," said Sarah Hart, director of the Justice Department's National Institute of Justice.
The federal government has allotted $28 million to help states reduce the DNA backlog. But two years after the money was made available, only half of it has been used. Even with the cash, some states simply do not have enough forensic examiners.
Last year, law enforcement authorities in Kansas City, Mo., received a $111,000 federal grant to reduce their DNA backlog. But police and forensic teams had to work weekends and nights -- 2,500 overtime hours for more than a year -- to get the job done.
In other states, officials say the federal money has been tied up in red tape.
After waiting 10 months for federal funding, Ohio Attorney General Jim Petro said he decided to spend the state's own money.
"Literally, it took us 10 months of weekly contact with the Justice Department only to find that there were still so many delays," he said. "Encountering that at every stage of the Justice Department process, we just went out and did it on our own."
The state of Ohio this summer paid four private contractors $605,000 and eliminated a DNA backlog of 19,000 samples in six weeks. As a result, 241 crimes were solved, officials say, including eight homicides and 80 sexual assaults.
Victims like Cunningham, however, want to know why a virtual treasure trove of evidence is not being better exploited.
ABC News' Pierre Thomas filed this report for "World News Tonight."