A 17-year-old boy has been detained for eight years for the killing of a pensioner during the London riots.
Darrell Desuze, of Bath Road, Hounslow, pleaded guilty at Inner London Crown Court last month to the manslaughter of Richard Mannington Bowes.
Mr Bowes, 68, was punched and fell to the ground as he tried to stamp out a fire in Spring Bridge Road in Ealing, west London, on 8 August.
He suffered brain damage when his head hit the pavement.
Desuze's mother Lavinia Desuze, 31, was jailed for 18 months at the same court for perverting the course of justice.
In a victim impact statement read out in court, the estranged sister of Mr Bowes, Anne Wilderspin, said she was "completely devastated to have found and lost her brother again in the same day".
She said Darrell Desuze had committed a "terrible crime" but added "I do forgive him".
"I feel compassionate for the youngster who was only 16 when he committed this crime which has potentially ruined his life," she added.
She said she hoped the teenager would be rehabilitated in a "loving environment and find a new purpose in life".
Nicholas Valios QC, defending, told the court Desuze "sincerely regrets and has remorse for all his actions, in particular his actions that led to the death of Mr Bowes".
The judge, Mr Justice Saunders, said he took into account the teenager's previous guilty pleas to burglary and violent disorder at William Hill, Tesco Express, Blockbuster and Fatboys Thai restaurant on the same night.
The judge said Desuze "played a full part in the violence" and could be seen on CCTV smashing windows, looting shops, throwing missiles at police and wheeling rubbish bins into the street so they could be set on fire.
He was caught on camera kicking in the glass doors of a shopping centre before joining a mob that attacked police with missiles.
The judge said most people were afraid to go out, and those caught up in the violence would have been "terrified".
"One person who was not terrified to be out and was not prepared to be forced off the streets was Richard Mannington Bowes."
"The death of Mr Bowes was pointless and unnecessary and it became for the public one of the most, if not the most, shocking event of the riots in London," he said.
CCTV showed the pensioner moving among the rioters and trying to prevent fires started in the bins from spreading, the judge said.
The court heard Desuze had once been on a school trip to the Metropolitan (Met) Police's riot training centre in Gravesend, Kent, where he watched a simulated riot during which officers were pelted with bricks.
It also heard the defendant's mother made a "very crude attempt indeed to interfere with the course of justice".
"This was a very significant fall from her moral character", the judge said.
But he added: "I do feel, as most people would, some sympathy for Lavinia Desuze.
"I accept that the instinct of a mother to protect her child is a very powerful one."
Following the sentencing, the Met's Ealing borough commander Det Supt Andy Rowell said: "Mr Mannington Bowes was an innocent man trying to do the decent and honest thing of protecting life and property; tragically he lost his life whilst doing so."
The Crown Prosecution Service's head of homicide for London, Daren Streeter, said: "This case will stand out as one of those which truly sums up the futility of the riots and the devastation that it brought to many of those who live in London."