CBS

Season 7: Episode 10 - The Bittersweet Science

The Bittersweet Science: ­After two men are found bludgeoned to death in an alley, the team flies to Philadelphia in search of a particularly brutal UnSub. Triggered by the imminent death of his terminally ill child, the killer â€" an amateur boxer with a history of losing â€" has been enveloped by an all-encompassing blood lust. As the window between kills starts to shrink, the BAU begins to run out of time.