The Weirdo by Theodore Taylor (1993, Paperback, Reissue)

They call Chip Clewt, who tracks bears, The Weirdo. But no one knows much about him. Only that he lives in the eerie swamp where Samantha Sanders found a body and where she saw another body get dumped.

Finally, she meets The Weirdo, sees his scarred face, looks into his tortured soul, and becomes his friend. Together, they begin the nightmare search for the killer who has stalked innocent victims, through the murky waters and dangerous marshes of the swamp.