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BROOKLYN (PIX11) –  Whatever happened to 15 year old, Bonnie Bickwit, and her high school sweetheart, Mitchel Weiser, who was 16?  It’s a mystery that still haunts their classmates from John Dewey High in Brooklyn, 40 years after they vanished.  Their families have never recovered from their disappearance.

“They were in love, and they saw each other all the time at school,” Weiser’s sister, Susan Weiser Liebegott, recalled for PIX 11 News.  “They were going to leave on a Friday to go to the Watkins Glen concert, which was starting Saturday, July 28th, 1973.”

Weiser actually hitchhiked upstate to meet Bonnie near Camp Wel-Met, where she was working as a mother’s helper for the summer.  The two planned to see a jam fest with the Allman Brothers, the Grateful Dead, and The Band.

“This was the big concert,” said Eric Greenberg, a journalist who was a teen in Brooklyn at the time.  “And my parents said: ‘Absolutely not.’”

Greenberg remembered the tabloid, front page headlines, when Bonnie and Mitchel failed to return home after the concert, even as upstate police and New York authorities argued it was unclear who should have jurisdiction in the case.

“The police comments at that time were like, ‘They’re probably just two hippie kids who got high and ran away to San Francisco.’”

Bonnie and Mitchel’s frantic parents searched for them upstate, in Canada, and made contact with police agencies around the country.  Mitchel’s sister even wanted to pose as a young person interested in joining a commune, hoping she could infiltrate a group her brother and Bonnie may have joined.

Susan Weiser Liebegott’s parents moved to Arizona but always kept a Brooklyn phone number that could forward calls to them.  About a dozen years after the couple vanished, the Weisers got a strange call at their Arizona home.

“A girl said, ‘This is Bonnie,’ and my dad was so excited,” Liebegott recalled.  “He said, ‘Oh my God, Bonnie! Bonnie! Where are you?’ And she hung up.”

Liebegott said she was never sure if the real Bonnie had called up — and then another strange development happened around the year 2000, nearly 30 years after Bonnie and Mitchel disappeared.  After a cable show about the case aired, a Rhode Island man named Allen Smith contacted New York State Police.

Smith told Major Case investigator, Roy Streever, that he’d hitchhiked with the couple after the concert and was riding in an orange Volkwagen bus on a hot day in late July 1973.  Smith told the trooper that the VW stopped near the Susquehanna River, so everyone inside could cool off.

The retired trooper recalled Smith’s story: “I believe the girl went in the water, Bonnie, and she started having trouble with the current.  And the guy went in after her, experienced the same trouble, and they got swept away down the river.”

The Susquehanna River eventually empties into the massive, Chesapeake Bay watershed, but Mitchel Weiser’s best friend, Stuart Karten, isn’t convinced they drowned.

“I don’t believe that’s what happened,” Karten told PIX 11, during a Skype interview from California.  “It’s really a tragic mystery.”

Karten started a website dedicated to Mitchel and Bonnie on the 35th anniversary of the couple’s disappearance.

This past July marked 40 years.  The Sullivan County Sheriff’s Department still has a detective that monitors the case.

“It is a long time ago, but I’m sure there’s someone out there who saw something or knows something,” said Michael Schiff, Sheriff of Sullivan County, where Narrowsburg is located.  “There’s somebody out there who knows what happened.”

About a dozen years ago, Allen Smith of Providence, Rhode Island said he was that person.  But until a body turns up, Susan Weiser Liebegott is holding on to a shred of hope her only sibling is still alive.

“You always want to know what happened,” Liebegott told PIX 11.  “To me, the truth is more important than anything else.”