I just don't see the suicide angle whatsoever. He knew that area. If he were suicidal, I don't think he's jumping off a ledge where an injury is a much more likely outcome than instant death. Even if he was drunk. If he was suicidal, he would go up to the Green Lane Bridge. I still haven't seen or read anything that makes me think anything but accident.
Whether Shane's death was due to foul play, suicide, an accident or sheer fluke, I earnestly pray that all his peers and classmates who maintained a vigil while he was missing remain vigilante in their own actions and honor Shane by taking a lesson from this tragic experience.