Police say Halton was "a totally innocent young man"
A gun used to shoot dead a 20-year-old man outside a takeaway has been linked to another murder, police have said.
Halton McCollin was shot in the head at the China Garden takeaway, Chester Road, Stretford, at 2100 GMT on 19 January 2008. He died three days later.
The silver revolver was used at the scene of the murder of Tyrone Gilbert in Chorlton-on-Medlock in July 2007.
The revelations come as Halton's father, Halton Senior, made an emotional appeal for information.
As well as the two murders, the gun was also used in a shooting outside a Bury pub in September 2007 and at the scene of an incident when shots were fired at a house in Cheetham Hill in August 2007, police said.
Greater Manchester Police has now increased the reward for information leading to the arrest and conviction of Halton's killer from £20,000 to £50,000.
Mr McCollin, from Bolton, has spoken out on the second anniversary of his son's death.
He said: "It's fresh in my mind. You wake up with it, you go to sleep with it."
"We miss him so much. It is unbelievable, like someone has switched a light off.
"He was such an outgoing person. He made friends at the drop of a hat. Male and female - people just wanted to be around him - he had magnetism."
Mr McCollin said he struggled to grieve without the closure of knowing who killed his son.
He does, however, believe the gunman will be found.
"I can only appeal on behalf of all of my family that that one person will come forward with that one small piece of information.
"It is not so much about being brave - it is just doing the right thing."
"I don't hold any malice. But there's a justice I want and I want a harsh justice.
"I am not the kind of person who believes they should be hanged, but I think when people take a life they should be locked away for the rest of their lives. That is what I want."
Three shots were fired at the Chinese takeaway, causing Halton and his friends, as well as the couple who owned the restaurant, to run for cover, police said.
One of the bullets hit Halton in his head causing injuries from which he never recovered.
Det Insp Kevin Greevy: "Halton was a totally innocent young man who was shot from behind in what was effectively a cold-blooded execution.
"Two years have now gone by and allegiances in that time will undoubtedly have changed.
"I would therefore urge those who know the identity of the gunman to think not only about the large reward on offer, but the devastating affect Halton's murder has had on his family."
He said the police would help protect the identity of people who came forward.
"When all is said and done a killer remains at large and if he has killed before then clearly he has the potential to kill again," Det Insp Greevy said.
"If you do have information, think about the potential lives you could save by helping us put this murderer where he belongs."