Death Grip - S2-E4
Plot hole: There is absolutely nothing that would give Horatio any reason to think the severed arm they found was from a previous victim of their suspect. It doesn't make any sense he would pick something as random as the arm that has no connection (other than it being found during the search for the girl) to the case.
Answer: Earlier in the episode, Horatio tells Mac that Penrod was seen in Tribeca getting his leg set, only to bolt when he learned a nurse wised up the cops. Caine and the NYPD probably got Penrod's address from the hospital.
Cubs Fan ★