Law & Order: Special Victims Unit 6x13

Quarry

When the body of a seven-year-old child is found, the squad again begins to investigate convicted serial killer Lucas Biggs, believing that he molested and murdered the boy. While Biggs can detail every child he ever molested, he swears that he has no memory of this one. Further investigations show that there is another suspect, but before he can be picked up, someone picks him off.