It was four days after Christmas in 1975 when the powerful bomb blew up at 6:33 p.m. in a baggage area in La Guardia Airport’s main terminal, which was jammed with holiday travelers. The bomb  equivalent to 25 sticks of dynamite  shattered plate glass windows 30 feet high, spraying glass shards like shrapnel, and hurled metal from shattered baggage carousels and coin-operated lockers.

Amid the smoke and debris, 11 people lay dead; 75 others were wounded.

It was the worst death toll from a bomb explosion in New York City since a bomb went off in a parked horse-drawn wagon on Wall Street in 1920, killing more than three dozen people and injuring hundreds. It drew condemnation from Pope Paul VI, local politicians and President Gerald R. Ford.

There were no credible claims of responsibility. No arrests were ever made. And though it remains one of the bloodiest, most puzzling chapters in the history of American terrorism, it has faded from public consciousness.

“It remains unsolved and almost forgotten  except by those whose loved ones were killed or maimed,” said Terence G. McTigue, a former supervisor in the Police Department’s bomb squad, who was among the first members of the force at the scene.