Tony Ferns was stabbed in Thornliebank, East Renfrewshire, on April 18, 2019.
The 33-year-old was sitting in his Audi A3 in Crebar Street when a man approached and attacked him.
Despite his injuries, Mr Ferns managed to make it home to Roukenburn Street, where paramedics fought to save his life, but he died with his mother Phyllis watching on.
A year on from the murder, Ms Ferns said: "I am pleading to anyone who may have information about whoever is responsible for my son's murder to please speak to the police.
"I can hardly put into words how devastated I am at the loss of my son. The pain I feel is unimaginable and while I know nothing will bring him back, I need to know who killed him and why his life was cut short."
Police have spoken to more than 600 people as part of the investigation, carried out more than 100 house-to-house inquiries and examined thousands of hours of CCTV footage.
On May 22 last year, four men aged 33, 44, 49 and 63 were arrested in connection with the death and later released pending further inquiries.
Officers now say they are convinced someone has information relevant to the murder, but may be too scared to come forward.
Detective Chief Inspector Grant MacLeod said: "Despite the passage of time, I am determined to find whoever is responsible for Tony's murder. It's clear he was a much-loved son and partner and is deeply missed by his family.
"I am convinced there are people out there who have information vital to this investigation who have failed to come forward.
"This may be down to fear or some misplaced loyalty to those responsible for this horrific crime, but please do the right thing and contact us, you can be assured your information will be treated in the utmost confidence.
"Phyllis had to watch her son Tony suffer and die, something no mother should have to go through. Put yourself in her shoes and think how she must feel, does she not deserve to know why her son was murdered and taken from her? Please help us find answers for a mother who deserves to know the truth."
Anyone with information is asked to call Police Scotland via 101, quoting incident number 4732 of April 18, 2019, or to call Crimestoppers on 0800 555 111.
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