Episode Description: Beware, spoilers! To read - hover over the text.
Dexter is involved in the investigation of the murder of Castillo. "Ice killer" Dexter watched during the violence and Jorge Vera. To substitute Dex he returned Vera body back to the crime scene, where he was found by police. Dex is forced to falsify evidence.
In the trunk of the car they found a little boy. Dexter realizes that it is - an involuntary witness to his crime, which must be "clean".