The body of 19-year-old Dean Geary was discovered by a passer-by on the A811 near Gartocharn, West Dunbartonshire, in the early hours of Sunday February 7, 2010.
A police investigation concluded that he died of severe head injuries after being hit accidentally by a vehicle.
But detectives say there are unanswered questions surrounding the case and are re-examining how Dean came to be fatally injured.
Mr Geary's father John, 46, from Alexandria, said: "It's every parent's worst nightmare, losing a child. Dean's room is exactly as he left it. We've been stuck in limbo."
Police have re-released CCTV footage of Mr Geary's last movements in Glasgow city centre.
He and his friend Mark Craig were seen arriving at Queen Street railway station for a night out on the Saturday.
He left the Tattoo nightclub alone at around 2am and was seen on CCTV in George Square at around 2.40am.