One week on from the deadly explosion in South Harrow and the cause remains a mystery.
A man died, another was injured and a teenage girl seriously burned when 21 Stanley Road blew up last Wednesday evening, obliterating the houses next door.
The Metropolitan Police were only able to begin their investigation in earnest on Monday because the scene of the blast remained unsafe for days.
Detectives want to discover what the mysterious purple liquid was that was poured through the letterbox of 21 Stanley Road on the morning of the explosion.
They will also probe a 999 call made around the same time by the teenage casualty - one of the occupants of the property which exploded - to report a group of nuisance girls outside.
In a further twist, although a gas leak has been all but ruled out as the trigger, neighbours have mentioned a historic smell of gas in the area.
Residents spoke vividly of the devastation they witnessed, the heroes who saved people from the rubble and the residents who remain homeless.