Brian Timothy Geraghty (born May 13, 1974) is an American film and television actor, best known for his roles as Ronald Pergman on Big Sky, Dale on the series The Fugitive, Gene Colder on Briarpatch, Theodore Roosevelt on The Alienist, Police Officer Sean Roman on Chicago P.D., Specialist Owen Eldredge in the Academy Award-winning film The Hurt Locker, Tom Bogdan in We Are Marshall, Billy Hodge in The Guardian, and Fergus O'Donnell in Jarhead.