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Grissom stuns the staff when he announces he is leaving the CSI team, but a murder which appears linked to the infamous Dick and Jane Killer is what has their attention. A body is found dismembered in trash bags along the creek, which is a similar motto of the killer, but he is in jail. Grissom attends a class held by pathologist Raymond Langston, hoping it will give him insight to this case.
Title: 19 Down...
The term 'X down, Y to go' refers to a sequential list of actions, or a set upon which a number of actions is to be performed, usually performed on the same type of object. In this case, it refers to murder victims of a serial killer. The grisly meaning is that 19 have been murdered, and (for part 2 of this two-part episode) one remains to be murdered.