for Chelsey and the Green-Haired Kid by Carol Gorman
Even though she could see the killer, Chelsey cannot convince the police that a boy's fall from the bleachers was no accident. Jack Smith, the green-haired kid, warns her not to investigate, but it's too late. Chelsey's being followed and somehow the green-haired kid and the girl in the wheelchair have to join forces to catch a murderer--before the murderer catches them.
Publisher description retrieved from Google Books.