Law & Order: Criminal Intent S06E14 - Flipped

Young rap artist Fulla T Smith is leaving a radio station after finishing an interview and debuting his latest hit song, when shots ring out in the lobby and he's killed. Detectives Logan and Wheeler question the one witness found on the scene, Harry Williams, who reveals he's an undercover cop whose task force specializes in crimes within the rap world. Williams warns Logan and Wheeler to watch themselves, but when he starts helping them out, witnesses turn up dead. The detectives begin to wonder which side he is on.