The most palpable, albeit unfortunate, explanation to Peter McColl's disappearance was a leap from the Golden Gate Bridge. People have been following false leads but the greatest obstacle to solving this case, by far, is political correctness and denial.
I remember the story rather well because my family ran a business on Berkeley's Solano Avenue, a few blocks from the McColl residence, and their mother shopped at our store, sometimes accompanied with her three children. I recognized Peter a few times and it was clear he was going through a personality change far from the common "teenage angst". He hung out on that street a lot, but the 1994 Solano Stroll was the last time I saw him there alive.
People who take their lives often create deliberate diversions for loved ones in order to "buy time". Cody's Books was a distance away from where the McColls lived and there were closer stores with a similar selection to choose from. In addition, he didn't bring any spending money with him. In other words, he had a mission that day and it wasn't shopping at a bookstore or anywhere else. My parents were also friends with the former owner of Cody's (now closed), his employees didn't report seeing the teen there on the date of his disappearance.
The reason the "cult theory" doesn't wash is because this tends to be the result of a lack of "belonging": people who find themselves marginalized by their family and lacking acceptance into mainstream society. Joining a cult also requires some preparation like extra clothes or money, since collateral is often stipulated for membership.
If he was murdered by drug addicts (an earlier theory) human remains would have turned up a long time ago. Drug addicts aren't good at disposing of crime evidence, especially not the street kids on Telegraph. Prolific serial killers are, but there's nothing to suggest Peter McColl was a victim of one.
Why do I stand by the "death by person" theory? Being a quiet, pacifist, high-achiever type who listened to rock music would have made a nasty experience for anyone attending East Bay public schools in 1990s; to inflate budgets and salaries, the superintendents allowed transfer students who not only resided outside the district but came from broken families. Many were also expelled from their previous schools. In their eyes, someone like Peter McColl would make a great target for bullying, and he was a week away from joining them again. Being 6' tall, having a group of friends or knowing martial arts wouldn't change the fact you would still be subject to nonstop harassment and potentially threatened with a weapon.
I didn't attend Berkeley (actually, another East Bay high school) and the general philosophy about this problem was to turn the other cheek and pity the troublemakers as "disadvantaged victims". It was an irresponsible approach to an affiliated vicious cycle; the transfer kids came from single mother homes while their more emotional targets lived in family structures lacking a strong, central father figure. Everything about the Peter McColl case (both before and after his disappearance) seems to suggest such, and what you often get is kids lashing out on themselves (self-harm, suicide) or towards other children (e.g. school shootings, inner-city/urban violence, etc.)
Even in late 1995/early 1996 when the case made local headlines, a jump from the GG was the most reasonable conclusion for Peter McColl's vanishing. It's an abrupt and sad way to go no doubt, but my ultimate hope is that his family acknowledges that's what probably happened and finds peace and closure.