THE explosion in South Harrow is not thought to have been caused deliberately, police say.
Forensic teams have been examining the site of the blast, in Stanley Road, and believe a build-up of gas in unused pipes in number 21 caused the explosion last Wednesday evening.
Officers have taken a section of pipe and the gas meter as well as the doormat away from the house for further examination.
Detective Chief inspector Colin Sutton, who is leading the investigation, said police have now ruled out theories that the explosion was caused by a purple liquid poured through the letterbox, and are focusing on gas as the cause.
He said: "None of the information gathered in the past few days supports the theory of explosives, or similar devices, nor a deliberate act to cause an explosion."
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