The businessman, who wants to remain anonymous, has donated £7,000 as a reward for information to catch Adam Chadwick’s killers – exactly seven years after he was fatally shot.
In addition to an existing Crimestoppers reward of £5,000 it means a total of £12,000 is now on offer to anyone who can help crack the case.
Adam’s father, Martin Chadwick, 54, said the cash donor was an old friend who he hadn’t seen for 30 years.
“For him to come forward and do what he has done is absolutely unbelievable,” he said. “I shed a tear when he told me what he wanted to do.”
Carpet fitter Adam, 20, from Seacroft, was visiting his sister, Gemma, on Clifton Mount, in Harehills, when three men burst into her house and shot him in the head on June 24, 2008. He died two days later.
The attackers were accompanied by a woman who had already been to the house asking to speak to a woman called Michelle.
Police have never managed to track her down.
Detective Chief Inspector Jim Dunkerley, who is leading the murder inquiry, said: “It may be that woman has an explanation as to why she was involved in what happened that night.
“I want to make a direct appeal to her to search her conscience, to think about the impact Adam’s death has had on his family and to come forward and tell us what she knows.”
The attack happened the day after Adam’s daughter, Ruby, turned three.
Gemma Wilson, regional manager for Crimestoppers in Yorkshire, said: “This is a horrific crime which has devastated a family and left a young girl without a father.
“It is still unclear what the motive was for this attack but Adam’s family deserves answers.”