The London house destroyed this week by a mysterious explosion was the target of a vandalism attack hours earlier when a purple liquid was poured through the letter box, police said yesterday.

Ten hours later, the house and two others in South Harrow, were razed in the blast. A man living next door, named locally as Emad Qureshi, 26, was killed.

Detective Chief Inspector Colin Sutton said a 17-year-old girl who lived in a flat in the property was the likely target of any attack. A girl was rescued from the wreckage and is being treated for injuries.

One nearby resident had called police earlier that day to complain about a gang of teenage girls gathered outside the house, who may have poured in the liquid.