A man who was shot dead in the street had once received a bravery award for intervening in a sex attack on a teenage girl.
Abraham Badru, 26, was gunned down in Hackney, east London, on Sunday.
Armed police were called to Ferncliff Road shortly after 11pm and found Mr Badru with gunshot wounds. He died at the scene.
His family say they are "beyond heartbroken" at his death, and revealed that he had been honoured in 2009 after helping secure convictions for the rape.
In a statement released through the Metropolitan Police, his family said: "Abraham was a very brave young man, he was the second to receive a Binney Memorial Award for his bravery and a Police Public Bravery Award, both issued by the police at a ceremony in Manchester on 8 July 2009.
"He helped the police in convicting some boys who had raped a teenage girl by being a witness in court.
"Not withstanding all the threats he received, he was bold and strong enough to do the right thing and make sure justice was served. He did his best and what was right in all circumstances."
Detective Chief Inspector Noel McHugh described Mr Badru as a "real contributor to society", adding: "Such courage and an overwhelming sense of what was right and wrong clearly demonstrated his strength of character."
Churchgoer Mr Badru had earned a master's degree in sports coaching at the University of Gloucestershire, and was hoping to pursue a PhD, his family said.
He had "never been involved in any fight", they added.
Paying tribute to a "beautiful soul", they said: "We are beyond heartbroken, filled with emptiness as we put together our feelings on our greatest loss.
"There is absolutely no reason for any kind of violence, it causes more pain than resolution. The gun culture is becoming rampant in our community and we all need to come together and put a stop to it."
Police say Mr Badru was approached by a "suspect or number of suspects" after he had got out of his black Mercedes opposite the green in Ferncliff Road, and was shot "without warning".
No arrests have been made.
Scotland Yard said Mr Badru's involvement in bringing the sex attackers to justice was a "line of inquiry", but that police were keeping an open mind about any possible motive at this stage.
Officers are looking to speak to anyone with information about the incident, or anyone who was in the area at the time.
Anyone who can help should contact the incident room on 020 8785 8099, via 101, or call Crimestoppers anonymously on 0800 555 111.