The family of a missing teenager turned detectives and uncovered CCTV footage of their son being chased over a bridge.

When police failed to find any trace of John Chipp two weeks after his mysterious disappearance his desperate parents launched their own investigation.

A murder inquiry is now underway after Ruth and George Chipp handed over the tape showing 18-year-old John being chased by a man in the small hours of March 19.

A 28-year-old man has been arrested on suspicion of murder.

Detectives are probing reports that John fell into the River Wear after a fight with a man on the Queen Alexandra bridge following a night out in Sunderland celebrating a pal's birthday.

Police frogmen were back at the river yesterday to continue searching for a body.

Detectives have asked city magistrates for more time to interview a 28-year-old man, arrested on suspicion of murder on Wednesday.

They were applying for a 36-hour extension to detain him for questioning.

No charges have yet been made.

Detective Superintendent Ian Sharp, who is leading the investigation, said: "We're trying to piece together what happened, but believe John Chipp has gone into the river following a fight with a man who chased him."

Trained police officers are comforting John's family in light of the new developments to the case.

His parents told how they were living in a nightmare because they didn't know if their eldest son was dead or alive.

They said John's disappearance was "completely out of character".

The search for John - known as Chippy to his pals - was first launched a fortnight ago when he failed to return to his Sheppard Terrace, Castletown, home following a night out in Sunderland.

The last sighting of him was at 12.20am on Friday, March, 19, as he crossed the bridge.

He was seen on the Deptford side of the bridge, but there have been no sightings of him on the Southwick side.

John was studying a uniformed services course at the City of Sunderland College and wanted to become a policeman.

He worked part-time at the McDonald's restaurant in Wessington Way.

He was a keen footballer who played left-wing for Hylton Castle boys, and had been in the city centre's nightspots on the night of his disappearance celebrating a friend's 18th birthday.

His parents have described the "nightmare" of not knowing whether their son is dead or alive.

George and Ruth, of Castletown, have appealed for more information from the public about their missing eldest son.

Mr Chipp, 45, said: "It's a nightmare because you're always wondering what has happened.

"Witnesses said they saw him jogging on to the bridge from the town side but no witnesses have seen him coming off the other side of the bridge.

"We know there are people crossing the bridge and there would have been night workers coming off their shifts."

Mrs Chipp, 43, a specialist nurse at Sunderland's Royal Hospital, said: "It is the not knowing that is the worst thing. It can be difficult to stay positive."

Both family and friends of John have been out on search parties between the mouth of the river and the A19 bridge.

Mr Chipp, a former miner at Monkwearmouth, said: "We just don't know where else to turn, as we have this stumbling block of the bridge and there are no cameras on the Southwick side."

He hoped people could have seen John, a uniformed services student at City of Sunderland College, in the Northern Way area of Southwick at about 12.30 to 12.45am.

John was wearing a light-coloured, long-sleeved shirt and pale trousers when he left home.

He is described as slim, clean shaven, with short red hair and about 5ft 8ins.

Mr Chipp said: "He had no reason at all to jump off the bridge."