Long after most New Yorkers had gone to bed, a crew of Verizon workers was on the streets early Tuesday morning getting ready to work on utility lines buried beneath the asphalt.

At around 3:15 a.m., they removed a manhole cover in a Midtown intersection and were hit by a putrid smell, they told a local news outlet. After descending, they were shocked to discover the source of the odor: a decaying corpse.

The gruesome discovery of a man’s decomposing body inside the manhole in a busy intersection created a subterranean mystery: How did the man’s body end up trapped in a space under a solid metal plate that can weigh as much as 300 pounds?

By Tuesday evening, investigators had uncovered surveillance video that provided a possible answer: It showed a man stumbling over barriers and falling into the manhole about two weeks ago, according to a police official.