Boston ? When three gunmen burst into a Chinatown social club and yelled “Robbery!” the men inside the club did what they were told, knelt down on the floor and put their hands behind their heads.

But one by one, five men were executed, shot once, twice or three times in the head, with guns that were held so close that they left gunpowder residue on the men’s clothing.

Nearly 15 years after one of the bloodiest crimes in Boston’s history, two men went on trial Tuesday.

Siny Van Tran and Nam The Tham are charged with fatally shooting five people and wounding a sixth man in the social club in Boston’s Chinatown section before dawn on Jan. 12, 1991.

Police said the killings appeared to be part of a dispute between rival gangs vying for control of Chinatown’s gambling rackets.