But the reasons behind the buildup are not entirely understood—the federal government has awarded research grants to Houston and Detroit to explore why so many have sat on shelves for so long. Law enforcement officials say there are some investigations where analyzing a rape kit is deemed unnecessary. And the new wave of testing and prosecutions comes with complications. As Ellen’s case demonstrates, victims, along with accused attackers, may face a traumatic journey into their dark pasts.

The math of the rape kit backlog is not simple. 400,000 untested kits do not equal 400,000 missed rape prosecutions. Only an estimated 50% to 60% of rape kits contain biological material that does not belong to the victim, according to a National Institute of Justice report. And police sometimes forgo rape kit analysis if the suspect was known to the victim or confessed, or when the victim is uncooperative or missing, says Asst. Chief Mike Slinkard, head of forensics for the Houston Police Department.

Nonetheless, testing a backlog of rape kits does lead to more prosecutions. More rape cases went to court in New York City after a cold case task force began sorting through old evidence in 1999. In Ohio, where Cleveland officials began analyzing 4,000 kits in 2009, resulting cases are now hitting the Cuyahoga County courts, where there are 58 rape kit-linked indictments now pending, according to the Cleveland Plain Dealer. Ellen’s case, which was the first to go before a Cuyahoga County jury, ended in late August. It illustrated many of the challenges in prosecuting old sexual assault cases.