John Kennedy, the 31-year-old brother of a boyband singer, was stabbed to death in Wapping, east London, on 8 February 1997.
The father-of-two was attacked during a night out with friends at the Railway Arms pub in Sutton Street at around 5.50am.
Witnesses were reluctant to talk to police at the time and the murder remains unsolved.
The case was referred back to the Homicide and Serious Crime Command following a review in 2010.
On 10 June 2013 detectives launched a fresh appeal for witnesses and offered a £20,000 reward for information leading to the arrest and prosecution of any suspect. The reward was later increased to £30,000.
Further appeals were made on 28 November 2013 and three days later a man handed in a note to St George’s Town Hall in Cable Street.
It read: “Around 2.55 – 3.00 early morning. Murder at the Railway Pub, Sutton Street.
“I was…waiting for someone… There was a fight. Knife was used by… The other bloke Kennedy plays football for the Falstaff pub. That’s how I recognised him.”
Detective Chief Inspector John Sandlin, said: “It is clear to us that the author of the note has some vital information that could assist the investigation into John’s murder. I would urge this person to contact the incident room so that we can speak to them. I would like to take this opportunity to reassure them they will be treated with the utmost sensitivity.”
In March 2014 the case featured on the BBC Crimewatch programme. A further appeal was made in February 2016.
John, a self-employed electrician and a keen local footballer, was on a night out with his friends when he arrived at the Railway Arms at around 3am.
At around 5.50pm he was confronted by a man he knew and a fight broke out in front of around 60 witnesses.
The suspect then pulled out a knife, lunged at John and stabbed him in the chest before leaving in a car with another man.
John, who was the brother of singer Jade Jones from the 90s group Damage, died in hospital at 8.20am.
He was living with his girlfriend in Oban Street, Poplar, at the time of his death and had two children.
John’s family said in a statement: “We would like to appeal for witnesses to come forward with any vital information regarding John’s senseless murder back in February 1997. Please help us to finally get justice for our loved one whom is forever missed and will never be forgotten.
“There are many people who witnessed this murder and have not spoken out due to either misguided loyalty or code of conduct. John’s life was taken away and the murderer should be held accountable for his death. Please find it in your hearts after 16 years to do the right thing and help bring the person responsible to justice.”
Detective Chief Inspector Ken Hughes, from the Met’s Homicide and Major Crime Command, said: “John’s family have spent the past 19 years campaigning for justice and deserve to know why such a level of violence was inflicted on him, leaving his two children without a father.
“I firmly believe that there are a number of people who are yet to speak with officers and who have information that will shed light on the events of that morning.
“I would urge them to come forward and speak with my team. It is possible that allegiances have changed and that someone who previously thought that they could not talk to us can now help bring this man to justice.”
Contact the incident room on 020 8345 3865 or Crimestoppers on 0800 555 111.