Maina stabbed 17-year-old Rizwan Darbar in the stomach during a mobile phone robbery in October 2007 in West Ham Park, east London.
The A-level student had been sitting in the flower garden of the park listening to music on the phone with two friends when he was attacked.
Maina was jailed for life with a minimum term of 14 years at the Old Bailey for the murder which Judge Timothy Pontius described as "an entirely needless and wholly unjustifiable tragedy".
Rizwan's brother Tausif Darbar said in a statement read in court: "My family's world was turned upside down."
Detective Inspector Simon Pickford said: "Rizwan was a young man with everything to live for."
The court heard that Maina's friend Kirkland Gayle had snatched a phone from a friend of the victim, then urged the knifeman to "poke" Rizwan so he would not have to give it back.
Alan Kent QC, prosecuting, said he did so, "jabbing the knife at fast speed into the stomach area of Rizwan Darbar".
Rizwan told his friends "I have just been duked" as the attackers ran off.
Gayle was jailed for eight years after he was cleared of murder but convicted of manslaughter and robbery.
Rizwan was preparing for A-levels when he was killed. He wanted to study accountancy and get a job in the City, and was a volunteer for events held in his area to promote the 2012 Olympics.
His brother said: "Rizwan was your average teenager - he loved his friends, football and music. He was extremely popular among both family and friends due to his great humorous personality.
"He was kind-hearted, generous and gave everybody the time of day. He was very obedient and respected and loved his family and friends tremendously.
"His death came as an immense shock as only a few hours earlier he was sitting at home with his family.
"The news of his death brought pain which no one should never have to suffer. The screams and my parents' faces that night still haunt me today.
"The loss of Rizwan was more painful with the knowledge that someone had taken his precious, promising young life due to their selfish actions.
"By their violent actions, they have torn our family apart."
Rizwan's family spoke of their grief today at the "senseless" murder of the teenager who was the second oldest of three brothers.
Tausif, 22, speaking from the family home in east London, said Maina had not shown any remorse and had laughed and exchanged jokes with co-defendants during his trial for the murder of Rizwan.
He said the family had no complaints "whatsoever" about the police investigation into his brother's murder.
"The case was extremely difficult from the onset, there was very little forensic evidence, there was very little CCTV evidence. If there is any criticism it is for the local authority for not having enough CCTV within the park," he said.
"The police did not leave a stone unturned in terms of the investigation."
Mr Darbar attacked the "culture of no comment" and said it was only after a key witness agreed to give evidence at the "last minute" that the police had been able to charge Maina for the murder of his brother.
He said: "Maybe if he had (agreed earlier) then maybe Jamie Simpson would still be alive."
Mr Darbar, a junior accountant who lives with his parents, Ayub, 48, a clothing wholesaler, his mother Mumuna, 45, and 17-year-old brother Yusuf, said Rizwan's death had "destroyed" the family.
"It has absolutely destroyed us as a family, he was the life and soul of our family, he was constantly having his friends over. It has destroyed my mother, her illness had got worse, and my parents are no longer the people they were before.
"It is difficult going to family gatherings - we have got a strong family around us but whenever we get together Rizwan is the first person we think about. There is not a day that goes by when we do not think about him."
Mr Darbar said he attended the second trial at the Old Bailey and met Jamie Simpson's parents.
