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.
At least 40 people remained in temporary hotel accommodation last night as the recovery operation continued.
Council officials said residents may face up to five of six days before returning to their homes.
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