A 'natural born killer' who knifed to death a Domino's Pizza delivery driver on his final shift, has been jailed for life.

Devastated relatives of Thavisha Lakindu Peiris questioned why Kasim Ahmed, 18, was free to kill the Sri Lankan, who was working for the takeaway pizza firm in order to pay off study debts.

Peiris was stabbed multiple times in Sheffield, Yorkshire, on his final shift before embarking on his dream career as a software engineer.

Ahmed already had a string of arrests for street violence on his record and regularly carried a knife for the purpose of carrying out robberies.

He targeted Peiris because he wanted his iPhone and attacked when Peiris refused to hand it over, stabbing the 25-year-old 14 times, last year.

Ahmed was jailed for life for murder at Sheffield Crown Court, along with accomplice and cousin Shamraze Khan.

Justice Coulson condemned Ahmed, saying: "In the light of your criminal history this was a murder that was waiting to happen."

Peiris' brother decried the fact his killer had repeatedly been turned loose by the authorities, despite his abysmal offending record.

"He was a natural born killer with a killer's instinct and should never have been allowed out of prison.

"He was clearly a very dangerous man and he should never have been released so he could kill normal people. It is shocking that he was allowed out on the streets to kill my brother."

Prior to his death, Peiris had been working 60 hours a week delivering pizzas in Sheffield, Yorkshire, to pay his family back for money they contributed to his studies.

Mr Justice Coulson told Ahmed: "You don't like to be challenged. It's an affront to your self-esteem. So you stabbed him. You then decided to stab him again and again."

"You brutally killed someone performing a form of public service just because you wanted his mobile phone," the judge said.

Peiris' family told of their pain in a statement: "We are now left with nothing but broken hearts."