Numb3rs Episode 3.15 End Of Watch

When the badge of an LAPD cop, who went missing in 1990, is found at a construction site, the FBI work with Lt. Gary Walker to reinvestigate the unsolved cop killer case. While Lt. Walker remains adamant that a former gang member turned activist killed the cop as revenge for killing his brother, Charlie analyzes the gang territory in 1990 and determines the cop was in a rival gang's territory and Lt. Walker has been focusing on the wrong suspect. Following this information, Don and his team weave though a tangled web of suspects including rival gang members, informants and dirty cops to ultimately find the killer.