POLICE have launched a fresh investigation into the unexplained death of a teenager whose body was discovered at the side of a road more than three years ago.

Dean Geary, 19, was found dead on the A811 near Gartocharn, West Dunbartonshire, in the early hours of Sunday, February 7, 2010.

The original investigation concluded the teenager, from nearby Alexandria, had died from severe head injuries after being accidentally struck by a vehicle.

However, the exact details of his death remain uncertain and police have now launched a comprehensive review of the incident.

Detective Chief Inspector Kenny Graham said: "Over three years have passed since Dean's death but I still believe there are opportunities to find out exactly what happened to him.

"Dean's body was found around seven miles from his home and it has never been established why he was in the Gartocharn area or how he got there.

"I believe there are still people who have information about Dean who have not yet come forward."

Mr Geary was working as a Ministry of Defence administrator at Coulport on Loch Long when he died.

He is thought to have left the Tattoo nightclub on Glasgow's Queen Street alone at around 2am. He was later seen on CCTV in George Square at 2.40am.

Mr Geary was then seen close to a taxi rank on the corner of Renfield Street and Sauchiehall Street at around 3.20am.

He then told a friend he was in a taxi at around 3.30am but his movements after that are unclear.

At around 5am, he was spotted by three motorists near Gartocharn as he walked along the A811 towards Drymen.

His body was then discovered by a passer-by on the same road, sometime during the early hours of Sunday morning.

As part of the new investigation, Police Scotland will work with the Crown Office and Procurator Fiscal Service in an effort to resolve a number of key issues.

First, it remains unclear how Mr Geary travelled from Glasgow city centre to Gartocharn.

Police are also eager to find out what happened to the teenager's wallet and Sony Ericsson mobile phone which have never been found.

Finally, investigators want to discover exactly how Mr Geary came to be fatally injured.

His death was initially treated as suspicious as police believed the teenager may have been the victim of an assault.

It was later concluded Mr Geary died as a result of being hit accidentally by a vehicle. Police said the incident was not suspicious and no charges were brought in connection with his death.

Later, in 2011, taxi driver John Ross was charged with wasting police time and misleading the original investigation.

He claimed Mr Geary had been murdered but was later taken to court accused of lying to investigators. Mr Ross faced a charge of ­wasting police time and rendering the public liable to unjustified suspicion of murder.

However, the Crown Office dropped the charges as an essential witness was unable to attend court due to ill-health.

Anyone with information about Mr Geary's final hours is asked to contact police on 01355 564083 or Crimestoppers on 0800 555 111.