A student was stabbed to death as he made his last pizza delivery before starting a new career.
Detectives say they cannot explain the "brutal and shocking death" of Thavisha Lakindu Peiris, who was found slumped at the wheel of his car on Sunday evening in the Southey area of Sheffield.
The 25-year-old was about to start a career as an IT consultant, police said.
Mr Peiris, a "career-minded, hard-working, bright, articulate and friendly young man", was making his last delivery for Domino's Pizza when he died.
He had been working for the chain's branch on Halifax Road in the city as he studied IT at Sheffield Hallam University.
Officers said he was delivering an order to an address in Southey Crescent which was due at around 10pm.
When he failed to deliver the order, his workmates set off to find him. He was found dead in the driver's seat of his silver Toyota Yaris. A post-mortem examination showed that he died from stab wounds.
Mr Peiris was born in Sri Lanka and had just successfully applied for a job as an IT consultant in Sheffield.
Sunday night delivery to the house in Southey Crescent was due to be his last before starting his new job.
A 50-strong police team is now working on the murder inquiry.
Detective Superintendant Lisa Ray, who is leading the investigation, said no motive had yet been established for the murder.
She said: "Thavisha Lakindu Peiris was a bright, hard-working, intelligent and caring man who had worked hard to develop his career in Sheffield.
"His murder is an absolute tragedy and has caused untold grief for his mother, father and brother in Sri Lanka and for his many friends in Sri Lanka and in Sheffield.
"Everything we have learned from his family, friends and workmates at Domino's suggests he was a career-minded, hard-working, bright, articulate and friendly young man who was very much planning his future. To date, we have found no explanation for his brutal and shocking death.
"I need to hear from anyone who knows anything about his murder."
The detective said: "We know that he set off in his car from Domino's at 9.50pm on Sunday night to make that very last delivery. At 10.30pm he was found dead in his car parked outside the address he was delivering to.
"It is urgent that anyone who saw him, or his car, or anything that they now regard as suspicious, comes forward without delay. A family is grieving for a young man 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."
Mr Peiris's family are preparing to travel to South Yorkshire, police said.
A number of people have been arrested and questioned by detectives since the murder but have now been released without charge, a force spokesman said.