The alleged killer of schoolboy Alan Cartwright was turned into police by his own family, a court heard on Tuesday.

Jurors heard Joshua Williams, 18, was found to have a copy of the New Testament after he was searched by an officer who described him as “polite and co-operative” after arriving at Islington Police Station.

He is standing trial for the murder of 15-year-old Alan in Caledonian Road on the evening of Friday, February 27. He was stabbed in the chest as he cycled with three friends.

Williams was taken to the station by his family on the morning of Wednesday, March 4, the court was told

His father allegedly told officers that Williams had owned up to the killing to his mother.

At Tuesday’s trial opening, the Old Bailey heard how three males, one of which is alleged to be Williams, had decided to rob Alan and his friends of their bikes.

But Williams, of Davenant Road, Holloway, now claims he was elsewhere at the time of the robbery, and denies murder and conspiracy to rob.

PC Chris Thompson said he was on duty just after 5am on March 4 when the family arrived at Islington Police Station.

He told the court on Tuesday afternoon: “I asked Mr Williams why he had brought his son to the police station. He said: ‘For him to hand himself in for the murder on Caledonian Road’.

“I asked him how he had come to the information. He said the defendant had told his mother about it.

“I explained to Joshua Williams that he would be arrested for murder. He was very upset and crying. He said: ‘This is the right thing to do, isn’t it?’”

Sgt David Smith, the station’s custody officer, was responsible for Williams’ detention after the arrest. He said: “He was very quiet, with real puffy eyes. He had been crying.”

Sgt Smith described Williams as “polite and co-operative”.

Williams was searched before he was detained. Among the items Sgt Smith found was a copy of the New Testament, he told the court. Williams requested that he kept hold of it, he said.

Jonathan Rees, prosecuting, had earlier told jurors of Williams’ alleged change in stance: “One can readily understand how a young man coming to terms with having stabbed someone to death might initially have been persuaded that the right thing to do was to hand himself in – before subsequently losing his courage when faced with the enormity of the consequences.”

The court heard Shaquille Roberts, 19, of no fixed address, and a 17-year-old boy have pleaded guilty to robbery for stealing bikes from two of Alan’s friends.

Mr Rees said the third robber, who the prosecution claim was Williams, stepped out into the road and stabbed Alan in the upper left part of his chest in a “deliberate and gratuitous stabbing.”

He added: “The robbery was brazen and swiftly executed, taking place in front of motorists and pedestrians. It was over in a matter of seconds.”

The trial continues.