Detectives think the same attacker was responsible for two other blazes.
They are linking him with fires at a Tulse Hill newsagent on 14 April and a South Norwood corner shop on 20 April.
Police chased the firebomb suspect, but lost him
“In the absence of any identifying motive, we are treating these offences as racial incidents.”, police say.
Officers at nearby Lambeth police station chased a man seen throwing an object into the Pricecutter shop but lost him.
The suspect is described as a black man, barrel-chested with a shaved head, aged 30 to 35, about 5ft 10in with a strong jaw line and rough skin.
Source: BBC News
