Four spectators were shot and wounded during a Massachusetts town's annual St Patrick's Day Parade after a fight broke out among two groups of young men.
Police said the violence erupted in Holyoke, Massachusetts yesterday as the last of 16,000 marchers completed the parade route.
More than 275,000 spectators turned out for the 52nd annual event, where security was heightened because of terrorism fears.
The alleged gunman was charged with assault. The names of the gunman and victims were not immediately released.
One of the victims, shot in the chest, appeared to have been the intended target, police said. He was in stable condition in hospital today. Three spectators standing near him, including two young women, were wounded in the legs. They were in good condition.
Police Captain William McCoy said police believe the shooting was related to a dispute that police had broken up shortly beforehand.
Holyoke is about 100 miles west of Boston.