"The Greenwich Village townhouse explosion occurred on March 6, 1970, in the Greenwich Village neighborhood of Manhattan. It was caused by the premature detonation of a bomb that was being assembled by members of the Weather Underground, an American radical left group. The bomb was under construction in the basement of 18 West 11th Street, when it accidentally exploded; the blast reduced the four-story townhouse to a burning, rubble-strewn ruin. The two persons preparing the bomb were killed instantly (Diana Oughton and Terry Robbins), as was a third "Weatherman" who happened to be walking into the townhouse (Ted Gold); two others were injured but were helped from the scene and later escaped (Kathy Boudin and Cathy Wilkerson)."
http://en.wikipedia.org/wiki/Greenwich_Village_townhouse_explosion