Twenty six-year-old Abraham Badru, who once received a Police bravery award, was gunned down in Hackney, east London, a few weeks ago.
Badru was praised after giving evidence against a gang which committed rape on the Frampton Park Estate in 2007.
Police said he was shot while opening the boot of his car to look for a drink.
The Metropolitan Police said just before the attack at around 11.10pm, Badru had parked his black Mercedes on Ferncliff Road when he was approached by a suspect or suspects.
He had not planned to be home at that time but had returned due to a change of plans.
Paramedics and police were called to the scene, but on their arrival, he was pronounced dead.
A black male, believed to be wearing a black puffer jacket, walked along Ferncliff Road in the direction of Downs Park Road and through a nearby alleyway after the sound of a gunshot, officers added.
His family has said they are devastated by his death, describing the pain as ‘unbearable.’
They added, “Abraham has been snatched from us; he didn’t die of an illness, a freak accident, or of natural causes, no death is ever easy but he died because he was shot.
“He was shot by person/persons terrorising the peace of the community, terrorising innocent people, threatening our freedom on our streets and threatening our progression.
“We plead with any parent, siblings, extended family, friends, associates, in desperation that if you have any information to please come forward.”
Police said Badru was described as a “talented young man with ambitions and so much to live for, but his life was cut short in his prime.”
Detective Chief Inspector, Noel McHugh, said: “The answer to Abraham’s death lies in the community. I know that people are talking about what happened.
“It is something truly out of the ordinary, a community hero being murdered.
“His family and friends cannot comprehend what has happened, and there are no words that can adequately describe the pain Abraham’s family are going through.
“Abraham was a striking young man and a real contributor to society. He was awarded a National Police Bravery Award in 2009 after intervening in a rape and then giving evidence in court.
“Such courage and an overwhelming sense of what was right and wrong clearly demonstrated his strength of character.”