6x13 - Quincy, M.E.

Polly Carmody, a young 9 year old girl, is murdered and found in a refuse bin. The police quickly pick up a suspect but Lt. Alex Markasian thinks that he doesn't fit the profile of a child murderer. He is much more interested in the fact that the 'father' of Polly is in fact her stepfather, and has only been in the house for a couple of months. When the arrested suspects blood type doesn't match the blood found on the victioms clothing Donald Thompson, the stepfather, becomes an even more likely suspect. This is made even more likely when Alex and Quincy discover some disturbing things in Thompsons' background.