Eleven people dead. Dozens more injured. When a bomb exploded in a public locker in LaGuardia on a December night in 1975, tearing a hole through eight-inch-thick concrete, it became the biggest act of terrorism in New York City in more than 50 years. Yet, another 50 years later, the tragedy has been all but forgotten. No one was ever charged. Nothing at the airport acknowledges the event. For Slate, Elon Green tracks down those who were there—and those who investigated—to figure out why, exactly, the bombing has slipped from the city’s memory.

In truth, despite the considerable effort expended by law enforcement, the investigation went cold nearly as soon as it began. “We’re grabbing for straws, trying to develop something,” an officer told the New York Times within 24 hours of the bombing. Because this was an era when the press often worked hand-in-glove with the police department, the failure wasn’t hidden from the public. Three weeks after the bombing, the Daily News reported that investigators “admit that thousands of hours of painstaking work have not put them on the track of anyone who could be called a likely suspect.” The chief of detectives, Louis Cottell, for his part, made no effort to hide how flummoxed he was by the killer’s refusal to take credit. “Why the hell would someone do this?” he asked. Years later, research would show that many terrorist attacks are neither claimed nor attributed.