What 1999 cult film follows two Irish brothers who become vigilantes?

The 1999 cult film about two Irish brothers who become vigilantes is The Boondock Saints.

Written and directed by Troy Duffy in his feature debut, the film follows Irish-American fraternal twins Connor and Murphy MacManus, played by Sean Patrick Flanery and Norman Reedus. After killing two Russian mobsters in self-defense, the brothers believe they have received a divine mission to eliminate criminals and begin a violent vigilante campaign in Boston.

Their actions are investigated by FBI Special Agent Paul Smecker, played by Willem Dafoe, whose flamboyant analysis gives the film much of its distinctive tone. The title refers to the brothers’ self-image as holy warriors, even though the film deliberately complicates the difference between justice, revenge, and vigilantism. It is sometimes confused with other crime films such as The Departed or The Town, but neither features this pair of Irish twin vigilantes.