Three years on from the unsolved murder of a Greenwich University student in Penge, police have released CCTV stills of two men they need to speak to.
Samuel Guidera, 24, was found collapsed in Bailey Place near Penge East station at 9.55pm on February 12 2011.
The history student, who had travelled on the 9.17pm Bickley to Penge East train, was stabbed in the heart and his wallet was stolen. He died in hospital that night.
But despite repeated appeals, four arrests and a £20,000 reward, nobody has been charged with the murder.
Officers believe Samuel arrived at 9.40pm before crossing the railway footbridge to the Newlands Park exit.
They now want to identify two men shown on CCTV arriving at Penge East on the 9.40pm train. They got on the train at Herne Hill and were seen walking towards the location where Samuel was attacked just minutes beforehand.
They took a similar route as Samuel, stopping at the junction of Venner Road and Newlands Park, before crossing the junction towards the bus shelter.
Detective Chief Inspector Chris Jones from the Met's Homicide and Major Crime Command said: "Whilst the two men have featured in extensive CCTV footage we have previously released they have not been identified.
"I believe they have vital information relating to Samuel’s murder and I am keen to eliminate them from the enquiry."
He added: "I would like to reassure anyone worried about contacting us that they will be treated with the utmost sensitivity."
Sam's parents Sarah and Chris said they were "serving a life sentence" after their son's death.
They said: "We still feel a sense of anger and all we can do is continue to cope with each day as it comes, with the help of medication, family, friends, whatever it takes.
"As parents we have seen the devastation and heartbreak it has caused Sam's brother and sister, other family members and friends.
"We just want somebody out there who knows something that could help in the apprehending of the killers to come forward so they do not have the opportunity to take another person's life and destroy another family.
"It could be somebody reading this who gets the call about the savage death of a loved one next."
They said: "So we miss and think of him so much every single day, we cry, we love him so much. Time is not a healer, we will never get back to normal; the people we were before no longer exist.
"So please look at your son, brother, uncle, think how you would miss them and if you know anything come forward - don't let the cowards who took my son's life kill again."
Police also want to speak to anyone who was around the Penge East shops between 9.40pm and 10pm that night. They have released CCTV images of the coming and going in the area that night.
Anyone with information should call 020 8345 3734 or Crimestoppers on 0800 555 111.