Nedim Yasar, a former gang leader who had turned his back on crime, was shot dead in Copenhagen just as a book about his life was published.
The motive for the attack in November 2018 remains unknown.
Now a court has found two men in their twenties guilty of his killing and jailed them for life.
Alexander Findanis was convicted of firing the shots and his friend Martin Binni Svanberg was found guilty of driving the getaway car.
Why this case is unusual
A life sentence is rare in Denmark and the pair are likely to serve at least 16 years in jail.
Both deny involvement in the attack and intend to appeal against the verdict. Police said they were satisfied the verdicts reflected the cold-blooded nature of the killing and relied on mobile phone evidence that pinpointed the pair as being in the vicinity around the time of the attack.
Marie Louise Toksvig, who wrote her late colleague's life story, said it was a waste of three lives but she was very happy the court had made the decision that "these two guys are the ones who did it".
However, the men's lawyer, Mai-Brit Storm Thygesen, said the prosecution had agreed with the defence that no motive had been proved for the murder.
Prosecutor Jens Povlsen said: "You don't need a motive to convict someone, you just need the evidence."
Ms Storm Thygesen argued the evidence against the pair was weak."Alexander Findanis was arrested almost a month after the killing and for that reason he was not able to recall what he did that night. From the [CCTV] video you cannot identify the face or anything," she told the BBC.
Findanis, 25, was described as a member of the Satudarah motorcycle gang and Svanberg, 26, admitted driving in the area at the time of the killing.
How Nedim Yasar left gang crime
Yasar, 31, was shot dead moments after leaving the launch event for the book about his story Roots: A Gangster's Way Out.
Marie Louise Toksvig's book detailed his journey into and away from gangland crime. Born in Turkey, he arrived in Denmark aged four and ran a notorious Copenhagen-based crime gang called Los Guerreros.
He eventually left the gang in 2012 when he found out he was to become a father and became a mentor for young people on local radio station Radio24syv.
Toksvig told the BBC she had known Yasar for three or four years, by which time he had already left his gang and worked through an exit programme with a view to getting the basic education he had missed when he was young.
"When I met him he was some steps on that bridge towards crossing over. And when he died he had almost crossed all the way over. He was in school wanting to get trained to work with helping young people like himself in the future," she told the BBC.
"Just over a year before he died, someone came to his door and tried to attack him with a knife. In his earlier days he would never have opened the door in the middle of the night without having a weapon in his hand. But when this happened he told me 'I'm just like you, I didn't suspect anything'. That told him and me quite a lot about his transition."
Toksvig said she had attended the trial to find out why Nedim Yasar was murdered. Although there were rumours that the men had been sent to carry out the attack, she said there was still no definitive answer.