Bob Keaton is Susie Keaton's abusive, drug-dealing husband. In "Big Brother", Horatio discovers that Bob's methamphetamine is the same batch as that used by Raymond Caine on the night of his alleged death. Despite his denials, Bob is convicted of Caine's murder and jailed.

When he is released (episode 320, "Killer Date"), it is revealed that he is an undercover DEA agent and Caine's ex-partner. Bob confirms to Horatio that his brother is still alive. His involvement in the DEA investigation and his knowledge about the Caine case leads to his murder (episode 322, "Vengeance").

He was played by Max Martini.