Police are appealing for help in solving the 30-year-old murder of a young detective stabbed by a bag thief he was chasing.
They believe there is still a chance to find the killer who vanished among the night-time traffic and streets busy with Christmas partygoers in central London in 1991 - and they are offering a substantial reward.
Detective Constable Jim Morrison, 26, was off duty and had just left a pub in the Strand to walk home when witnesses saw him trying to arrest a suspect near the Covent Garden piazza.
The man, thought to be a young North African, pulled out a knife and ran off as the officer threw off his coat and jacket and chased him.
After a pursuit into Aldwych, the suspect stopped beside the Indian High Commission, turned and stabbed unarmed DC Morrison three times.
An international manhunt led to inquiries in France, Belgium, Germany and Canada and several suspects were arrested, but no one was ever charged.
The officer had been married for three years, had joined the Criminal Investigation Department around the same time and was already earning a reputation for a flair for tackling street crime.
His widow Victoria is still haunted by the futility of the way in which he died.
She said: "We had talked about the risk because of the job he did, but you never think it's going to happen to you. It was devastating, life-changing for me and Jim's family and all who knew him.
"It was a complete waste of a life, over a handbag, but being a police officer Jim always wanted to do the right thing and be law-abiding.
"At the end of the day people carry knives and are willing to use them at all costs. They simply don't value life.
"I hope we can find the man who did this. Anyone who commits a crime like this would have to tell somebody, so there are people who know what happened and I would like them to come forward and tell it. Even after all this time it would mean everything to me and Jim's family."
It was a Friday night two weeks before Christmas, the streets full of pub-goers and theatre crowds spilling out of evening performances, so plenty of potential witnesses to the chase and the murder.
The suspect was described as in his late 20s, 5ft 10in tall and appearing to be North African, possibly Algerian. Police spoke to many people in those communities in London.
Detectives believe the killer was part of a gang that had been stealing bags from pubs across the West End.
Detective Chief Inspector Rebecca Reeves said: "The suspect was telling Jim that he would hurt him, but regardless of the risk to his own safety he continued to chase him and try and stop the crime that had happened.
"I relate it to the dangers that police officers face today in London and I feel that connection with what he did that was so selfless and that gives me the determination to make sure this investigation goes on.
"Jim would never have given up and neither will we. I want to reach out to people around the world because there has to be the strong possibility the suspect or someone who was part of that group is still out there."
There is a £30,000 reward for information that leads to an arrest and prosecution.
Members of the public can provide information via a portal.
They can also call detectives on 020 8785 8267 or contact Crimestoppers anonymously.