A DANGEROUS obsessive – described as a “bedroom Rambo” – was behind bars last night after being convicted of making a pipe bomb at the school where his father worked as a caretaker.

Remanding David Riding into custody until a psychiatric report can be prepared, Judge Christopher Prince said the pony-tailed biker was extremely disturbed, and linked his secretive actions to US-style high school massacres.

A bomb disposal team was called to Durham High School for Girls in November last year, when police discovered a 13cm-long copper pipe bomb hidden in a locked safe under Riding’s bed.

The home he shared with parents, Keith and Karen, lies within school grounds.

Yesterday, Judge Prince envisioned a chilling scenario where Riding, now 20, would walk into the school armed with his home-made bomb and other weapons.

Riding, who made the bomb using information he found on the internet, claimed he manufactured the device to see if it could be done.

But the judge described this as a “blatant lie”, pointing out he wrapped tape around part of the bomb to protect the user’s hands, and waited two to three months for pyrotechnic powder he extracted from commercial fireworks to dry before putting it into the device.

Riding scratched “killer” on the bomb, which was found with two imitation firearms, three knives, a knuckle-duster and blank rounds.

Following a three-day trial, a jury of nine men and three women took only 35 minutes to convict him unanimously of making an explosive substance without a lawful purpose.

Ian West, for Riding, sought to portray his client’s actions as stupid, and motivated only by curiosity. Riding claimed he never planned to explode the device.

Closing the case for the defence, Mr West said: “Might it not just be that he is a bedroom Rambo? That he likes to have guns, running around the woods with them going ‘bang, bang’, which he’s entitled to do, and just went one step too far in making that item?

“Might it not just be that he’s a daft lad from a good home who really ought to spend less time on the internet and get out more, instead of spending his time making items like this?”

But following Riding’s conviction, the judge said: “I believe this is an extremely disturbed young man. I am far from convinced he does not pose a very real risk to the public.

“He has taken time and effort to create a nasty weapon.

“He was living at a school.

There have been the most appalling tragedies within schools, created by people going in armed with weapons.

“He would have had such a stock of weapons, he would have been in a position to go into the school with knives stuck in his belt and a knuckleduster to protect himself, two guns which looked very realistic, 47 cartridges and an improvised explosive device that may have had a lethal capability, scrawled upon which are words which demonstrate some form of resentment to other persons, namely ‘killer’ and other obscenities.

“This is a 19-year-old man, now 20, with a potentially lethal weapon in his bedroom.

I find it very disturbing.”

Turning to Riding, the judge said: “I take the view that there’s a very high likelihood of you receiving a custodial sentence for your creation of this improvised explosive device, which you kept with a number of other items which were capable of being used as weapons or to frighten.”

Riding learnt how to make pipe bombs while a pupil at Durham Johnston Comprehensive School, using a school computer to access a website offering instructions. He built the device in early 2006.

A forensic scientist told the trial that the copper piping may have produced shrapnel, which could have caused injury.

Riding, who worked at a Homebase store and later Houghton Hardware, kept the existence of the bomb from his parents because he feared it would jeopardise his father’s job.

He was not present when police, acting on information, arrived to search his home in Lake View, Station Town, in east Durham. Riding’s parents gave evidence during his trial. As he was led from court yesterday, his mother wept in the public gallery.

Riding will be sentenced on Friday, January 23.