Cultural References
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.