A 15-year-old boy who followed a teenager he did not know through Birmingham city centre and stabbed him to death after a four-minute conversation has been jailed for life with a minimum of 13 years.

Muhammad Hassam Ali, known as Ali, was 17 when he died in hospital on 20 January, hours after he and his friend were confronted by two masked 15-year-old boys they had never met as they sat in Victoria Square, drinking hot chocolate and chatting about cricket.

The two boys, who cannot be named for legal reasons, had followed Ali and his friend from the Grand Central Shopping Centre wearing Covid-style face masks.

Neither of them showed any emotion as they were sentenced by the judge, Mr Justice Garnham, who said 17-year-old Ali’s murder was “yet another illustration of the appalling consequences of carrying knives in public places” as he detained them at Birmingham crown court on Friday.

He said: “It is perfectly clear to me (Ali) was a much-loved son and brother and his family have been left utterly devastated by his death.”

He sentenced the second boy to five years’ detention in secure accommodation.

A trial at Coventry crown court earlier this year heard that, in a conversation lasting about four minutes, the two boys asked Ali and his friend where they came from and if they knew who had “jumped a mate” of theirs a week before. After Ali allegedly said: “Bro, I don’t know what you’re talking about, you’re pissing me off,” the youth pulled out a large knife and stabbed him in the chest.

A jury took just over four hours to return unanimous verdicts in July, finding the youth who carried out the fatal attack guilty of murder and possessing a knife and his friend, who was standing nearby when the stabbing happened, guilty of manslaughter and possessing a knife.

In his evidence, the teenager who wielded the knife told the court he only wanted to “scare” Ali and his friend, and that he did not intend to seriously harm or kill anyone.

Michael Ivers KC, representing the defendant, said he was remorseful and prays for Ali and his family regularly.

He said: “He isn’t a man who is in any sense proud of what happened. He truly, truly regrets what happened.

“If he could turn the clock back, not for his own sake but because of the impact it has had on others, he would.”

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Sentencing the pair, who sat in the dock wearing white untucked shirts and dark trousers surrounded by four dock officers, Mr Justice Garnham said the knife had been pulled out “for no obvious reason”.

He said: “You suggested in evidence that the words of Ali caused you to fear for your safety. The jury did not accept that and neither do I.

“They did no more than was reasonable in trying to persuade you to go away. There was no justification for pulling out a knife on an unarmed young man who posed no risk to you.”

A statement from Ali’s family, who were in court for the hearing, read out by prosecutor Mark Heywood KC described the teenager as a budding engineer and said they would never get over his death.

They said: “The loss of a child is devastating and life-destroying, but the fact someone took his life in such a horrific and brutal way will always haunt us.”