Complex sentence: An associate, Brian Halloran (Peter Sarsgaard), goes to the FBI to report Whitey's involvement, much to Connolly's displeasure, who then tells Whitey of Halloran's accusation, thereby resulting in the murders of Halloran and an unnamed accomplice.
Split into simpler sentences: An associate, Brian Halloran, goes to the FBI to report Whitey's involvement. Connolly tells Whitey of Halloran's accusation, resulting in the murders of Halloran and an unnamed accomplice.