Police are investigating a purple liquid that was said to have been poured through the letterbox of a house that was ripped apart in an explosion in north west London on Wednesday.
Three terraced houses were flattened and a man was killed when the explosion ripped through Stanley Road, South Harrow.
The blast, which left two other people suffering serious injuries, was first thought to have been caused by a gas leak.
But engineers found no fault with the gas mains supply.
The body of the dead man - named locally as 26-year-old Emad Qureshi - has been recovered from the scene and a post-mortem examination is due to be carried.
Earlier it emerged a woman whose home was destroyed had called police to complain about the behaviour of a group of girls on the day of the explosion.
The blast reduced number 19 and two flats at 21 to a pile of rubble, and number 23 was ripped out with only part of its adjoining wall left standing.
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