They said Kennie knew the group was in the area and passed them as he walked home.
“At that moment, he became their focus,” they added.
The force said more than 20 warrants were executed during its investigation and a number of appeals were made, one of which offered a £50,000 reward.
Six others teenagers, who were aged between 15 and 19, were found not guilty of charges related to Kennie’s death.
Following the convictions, Kennie’s mother Joan Dixon said he had “brightened up every day with his cheeky smile and bubbly personality”.
“He was always acting daft, telling jokes and generally being a 16-year-old boy,” she said.
“He had everything to live for.”
She said he was the youngest of four children and was about to start applying for college to pursue his passion for designing artwork on cars.
“He was a very talented artist,” she said.
“I hadn’t realised how artistic he was until one of his teachers showed us his drawings and they were genuinely impressive.”
She said life since the day of his murder had “not been the same”.
“Every day I wake up thinking of him. I dream about him regularly,” she said.
“Life has stopped for us and will never ever be the same.”
Det Ch Insp Nicola McCulloch said it had been “extremely difficult” to get those responsible for the “spiteful attack” in court and their continued denials had caused Kennie’s family further pain.
“They’ve had to watch and listen to Kennie’s last moments many times,” she said.
“[That is] something no family should have to experience.”
Sentencing will take place on 26 July.
