A teenager murdered in south London was a "model athlete", the secretary of the sports club where he trained has said.
Sylvester Akapalara, 17, of Streatham, was shot in a stairwell on the Pelican Estate in Peckham on Wednesday.
"He showed no signs of being in any trouble - that's why we are so shocked," said Steve Bosley of the Herne Hill Harriers.
Two males are being held over the attack. Two stabbings have also been linked to the shooting.
Mr Bosley said the 400m runner was nationally ranked "in the top 30 or 40" in his events, and joined the club - based at Tooting Bec, south London - when he was 12.
"He was very highly ranked at that age," he said.
"He was first spotted by a PE teacher at his primary school."
He said Sylvester, a Sierra Leonian national, "was doing quite well academically" and had been told to be "more aggressive in his running and more positive about himself".
Team managers had described him as "quiet and unassuming", Mr Bosley added, and a memorial would be organised for him in due course.
More than 760 people have joined a Facebook group set up in memory of the teenager, who was also known as Sylvester Da Donappa.
He was found bleeding to death on the fourth floor of Heron House on the Pelican Estate and had been shot in the neck and chest.
A second 17-year-old boy was found with stab wounds in a flat in neighbouring Gannet House.
An 18-year-old man went to King's College Hospital with minor injuries.
Both have since been allowed home.
Three teenagers were arrested shortly afterwards.
Two of the three have been released with no further action to be taken, while the third has been bailed until late January.
Two further youths who were arrested, aged 17 and 18, remain in custody.