“Boss” star Troy Garity has joined the cast of Warner Bros./Village Roadshow’s period crime pic “The Gangster Squad.”Garity will play a one-eyed hitman dispatched by gangster Sean Penn to kill characters played by Ryan Gosling and Josh Brolin. Ruben Fleischer is directing from a script by Will Beall, and production is currently under way in Los Angeles. Garity, who was one of Variety’s Top 10 New Faces for Fall TV, will soon be seen playing an investigative reporter going after Kelsey Grammer on Starz’s “Boss,” which has officially upped him to series regular. He recently played a vengeful mobster on NBC’s canceled series “The Playboy Club.” Thesp, whose turn in the 2003 telepic “Soldier’s Girl” earned him a Golden Globe nomination, will film “Gangster Squad” into December. His previous feature credits include Danny Boyle’s “Sunshine,” Barry Levinson’s “Bandits” and Tim Story’s “Barbershop.” Garity is repped by CAA and Untitled Entertainment.