The court heard that the boy told police in a pre-prepared statement that he had confronted Mr Kohli because he thought he had been threatening children in the park with a flick knife.
In an account given to a paramedic at the scene, Mr Kohli had said the boy had called him a racial slur, then punched and kicked him as the girl watched.
Harpreet Sandhu KC, prosecuting, told the court that the boy had put on a balaclava in preparation for the violence he was about to inflict on Mr Kohli.
A 15-year-old boy is charged with Mr Kohli's murder and manslaughter, while a 13-year-old girl is charged with his manslaughter.
The first showed Mr Kohli on his knees in the park as a youth slapped him across the face with a slider shoe.
