A 68-year-old man suffering critical injuries while trying to extinguish a fire during riots in west London died, Scotland Yard said.
On Monday night, Richard Mannington Bowes suffered head injuries in an attack in Ealing, an area in west London. It had left in a coma.
Bowes is the fourth person to die in the recent disorder - three men died in Birmingham after being hit by a car while protecting property Tuesday, BBC reported.
The Scotland Yard launched a murder inquiry and issued a CCTV image of a suspect in the Bowes' case.
The other three - Haroon Jahan, 21, Shazad Ali, 30, and Abdul Musavir, 31 - were struck as they stood in a crowd on the pavement in Winson Green, Birmingham.
On Thursday, West Midlands Police said two boys, aged 16 and 17, and a man, 26, were arrested on suspicion of murder.
On Thursday, Britain's Prime Minister David Cameron said police admitted to getting their riot tactics wrong.
Cameron said his government could consider using the army to deal with future riots and may allow police to block social networks and force people to take off masks, RIA Novosti reported.
He was speaking in the wake of riots and looting that hit several British cities and left 111 police injured Aug 6-10, Scotland Yard said.
"It is the government's responsibility to make sure that every future contingency is looked at, including whether there are tasks that the army could undertake that might free up more police for the front line," Cameron told an emergency parliamentary session.
Cameron said the government will compensate people whose houses or businesses were damaged in the riots.
He also said police might be allowed to interfere with internet networks and other telecommunication devices if any suspicions arise.
Over 1,300 people were arrested since the unrest began Saturday.
Addressing the House of Commons, Cameron announced a 10 million-pound package to deal with the damages caused by rioting in various towns and cities.
Violence began August 6 in the British capital's northern district of Tottenham over the fatal shooting of Mark Duggan by police. The unrest quickly spread to cities like Manchester, Salford, Liverpool, Wolverhampton, Nottingham, Leicester and Birmingham.
The prime minister said "keeping people safe is the first duty of government."
