A young man killed in a car accident in 1995 has finally been identified - after internet sleuths took up the investigation 20 years later.

The body of Jason Patrick Callahan, whose identity was unknown for two decades and was dubbed "Grateful Doe", was found in a car which had crashed into trees in Virginia.

His mother, Margaretta Evans, reported him as missing only this year after an internet campaign on Reddit and Facebook to identify him reached mainstream media.

Mr Callahan had not been seen since setting out for a rock concert 20 years ago, when he was aged 19.

When authorities found the crashed car, he had two concert tickets to see rock band The Grateful Dead and was wearing a T-shirt bearing the group's name. The American rock band is closely associated with the "hippie" movement of the 1960s and '70s.

A star tattoo and a Grateful Dead T-shirt were two clues for identifying the young man (YouTube, ABC)

A letter was found at the crash site, which read: "Jason, Sorry we had to go, see ya around, call me #914. Call me, Caroline T and Caroline D. Bye!!!!"

Authorities were unable to trace the area number or the two women, while the young man's fingerprints were not found on the national database.

The driver of the car, 21-year-old Michael Hager who also died, did not appear to have connections with "Grateful Doe" and it is now thought he may have picked Mr Callahan up as a hitchhiker.

Mr Callahan had a homemade star tattoo on his left arm, but without other distinguishing features he became known as "Grateful Doe" - a reference to the band and John Doe, the name traditionally given to unidentified dead bodies in the US.

But after a volunteer effort through The Doe Network's Facebook page and Reddit led to police re-launching pictures of him this year, Ms Evans contacted Myrtle Beach police to say she recognised images of her son in mainstream media, according to the New York Post.

Police then carried out DNA testing to confirm the body, which was unrecognisable after the crash, was Ms Evans' son.

Mr Callhan's half sister, Shannon Michelson, told Fox News she was both relieved and sad that the circumstances around her brother's disappearance had been brought to light.