Michael Parisi (alias Pizza Face) is a young pyromaniac and an accused serial sexual assailant of little girls in the Bronx. Parisi was never convicted on three different charges due to the girls never wanting to come forward and testify, but Parisi would make a habit out of finding arsons for the sake of getting aroused from being a spectator.
Parisi was suspected of the fire that killed Faye and Kedzie Sullivan, from being a witness taking pleasure from being a short distance away from their burning house. Parisi was arrested and his record pulled up, with Stabler getting a confession of molesting and burning the sisters by lighting matches and burning paper in a trash can to tantalize it out of Parisi. It wouldn't have held up in court, thus Parisi was released.
It was revealed the fire was an accident due to a space heater, which nearly got the girls' father, Frank Sullivan, falsely convicted on arson charges due to incomplete forensics. (SVU: "Torch")