Mr Dolby, speaking outside at Inner London Crown Court where Desuze, who was 16 at the time of the killing, admitted to manslaughter went on to say and that the case "sums up the futility of last summer's riots".
Mr Mannington Bowes had been trying to extinguish fires started by Desuze and the gang of rioters, in Ealing, west London, on August 8 2011.
The schoolboy punched the 68-year-old retired accountant with such force that he was knocked out. He suffered fatal brain injuries as he hit his head on the road.
Mr Dolby said that the Ealing pensioner was "simply trying to prevent further damage".
"In a single moment a man suffered devastating injuries," he said, adding he hoped the conviction of the teenager would provide some comfort to the family.