An “intelligent and caring man” who delivered pizza to support himself through university was murdered while making his last ever delivery before starting a career in IT.

Police said Thavisha Peiris, 25, was found stabbed to death in his car in Sheffield just 40 minutes after he left the Domino’s Pizza outlet where he worked on Sunday night.

Detective Superintendent Lisa Ray, head of a 50-strong team looking for the killer, said they did not know why Mr Peiris had been killed. A small amount of cash was still with him in the car. Police said there was no evidence of a racial motive, but could not rule anything out.

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“Thavisha was a bright, hard-working, intelligent, caring man,” Det Supt Ray said. “He was friendly and career-minded, working to develop his career. His murder is an absolute tragedy and has caused untold grief for his mother, father and brother in Sri Lanka.”

Mr Peiris, who came to the UK from Sri Lanka in 2011, left Domino’s in a silver Toyota Yaris at 9.50pm to make the delivery to an address in Southey Crescent about a mile away.

Ravi Marripudi, his manager, said that Mr Peiris had not been “feeling very well” and “wanted to go home”.

“But he said he would deliver this last one,” he said.

Mr Marripudi said that 15 minutes later the customer called to say that the order had not been delivered.

Another driver was sent to look for Mr Peiris, who was found unconscious in his car, parked in a residents’ parking bay near the delivery address, at about 10.30pm.

Mr Marripudi said the murdered man was “such a kind person”.

There were reports that four delivery drivers had since decided to quit the branch, but Domino’s said last night that no one had formally handed in their notice.

A spokeswoman for Domino’s said in a statement: “Staff both in the store and also around Sheffield are deeply shocked at this senseless murder and it has understandably unnerved them,” adding that they would be offered “individual and tailored support”.

At a press conference, police said a number of people had been arrested and questioned, but all had been released without charge.

Det Supt Ray said: “The attacker will have gone home on Sunday night, or early hours of Monday morning, with blood on their outer clothes. Did someone you know start behaving out of character, washing their clothes, appear to be highly anxious?

“A family is grieving for a young man who whose life has been taken from him in the most brutal of fashions, and we owe it to him and his family to find the person or persons responsible.”