A 15-year-old boy has been found guilty of murdering a man stabbed to death outside an Asda supermarket.

Ian Kirwan, 53, was attacked at the store in Redditch, Worcestershire, on 8 March after challenging teenagers for messing about in the customer toilets.

Two youths aged 14 and one of 16 were cleared of killing Mr Kirwan, but were found guilty of violent disorder, while a fifth, 16, was cleared on all counts. 

The jury heard the killer was part of a masked gang that "terrorised" people.

None of the four boys can be legally identified because of their ages, and are due to be sentenced on 15 February.

Mr Kirwan, an artificial intelligence engineer at Jaguar Land Rover in Coventry, died after being stabbed in the heart.

Birmingham Crown Court heard he had gone to Redditch to buy a light switch from B&Q and had simply used the toilets at Asda. 

Joe Fitzpatrick, a friend of Mr Kirwan, said his death had had a devastating impact on the whole family. 

The killer, from Birmingham, aged 14 at the time, had travelled with four other boys by train to the town on the day and subjected Mr Kirwan to a minute-long attack near the entrance of the store.

He had admitted the stabbing, but claimed diminished responsibility. However, jurors convicted him of murder.

Mr Kirwan was an "unfortunate member of the public in the wrong place at the wrong time", jurors were told during the 10-week trial. 

The fifth defendant was acquitted of murder, manslaughter and violent disorder, having claimed he was not involved in the fatal confrontation and could not have predicted it. 

High Court judge Mr Justice Fraser told the 15-year-old who was convicted of murder: "I know that your counsel will have explained this to you already - you are going to be sentenced to the youth equivalent of a life sentence.

"But I am not going to pass that sentence [now] because I have to fix the minimum term. I am going to do that on the 15th of February

Det Supt Leighton Harding, senior investigating officer for West Mercia Police, said it was "an appalling attack on an innocent man going about his daily life".

"I'm pleased that justice has been done today for Ian and our thoughts remain with his family and friends, who have shown incredible strength throughout the investigation and the trial."

He said the force had an "incredible" response to its appeals after the murder, which led to critical information being gathered and convictions being secured in an "incredibly complex" case.

The danger of carrying a knife was "painfully obvious in this very sad case", he added.

Peter Martin, an anti-crime campaigner in the town, said the killing had had a huge impact on the community and witnesses had been offered free counselling. 

"This was just a guy, just going shopping - so the impact on the community was massive," he said.

Many local residents had been affected, he said, particularly other shoppers who had witnessed the stabbing.