Before Columbine, Virginia Tech, Aurora and Newtown, there was the Long Island Rail Road.

On Dec. 7, 1993, a gunman opened fire on a train car filled with commuters leaving New York City. By the time passengers tackled Colin Ferguson, his fusillade had left six people dead and 19 wounded.

Though other massacres have far superseded it in terms of casualties, there are aspects of the railcar shooting that, even two decades later, make it stand out in the sad pantheon of rampages that have horrified the nation.

“In a mall or a school or a movie theater, there is at least some opportunity for hiding or escaping,” said James Alan Fox, a criminology professor at Northeastern University in Boston. “These people had nowhere to go.”

And then there was the trial. Ferguson defended himself in court, cross-examining the very people he terrorized.

Ferguson, who boarded the train in Queens, claimed that he waited to open fire until the train crossed over the New York City border out of respect for David Dinkins, the mayor at the time. He fired methodically over several minutes, reloading at least once, before the train arrived at the next station, where terrified survivors ran screaming from the exits.