“Robert Spada walked into the decrepit warehouse in Detroit and surveyed the chaos: Thousands of cardboard boxes and large plastic bags were piled haphazardly throughout the cavernous space. The air inside was hot and musty. Spada, an assistant prosecutor, saw that some of the windows were open, others broken, exposing the room to the summer heat. Above the boxes, birds glided in slow, swooping circles.

It was August 17, 2009, and this brick fortress of a building housed evidence that had been collected by the Detroit Police Department. Spada’s visit had been prompted by a question: Why were police sometimes unable to locate crucial evidence? The answer lay in the disarray before him.

“I’m assuming they’ve been tested?” Spada said.

“Oh, they’ve all been tested.”

Spada pulled out a box and peered inside. The containers were still sealed, indicating that the evidence had never been sent to a lab. He opened four more boxes: the same.

“I tried to do a quick calculation,” he later told me. ‘I came up with approximately 10,000.’”