Officers had been investigating the incident as possible murder after initial enquiries suggested a substance poured through the letterbox of number 21 Stanley Road might have caused the explosion.
But, police have now said no evidence points to this being a factor.
Detective Chief Inspector Colin Sutton said in a statement: 'We are now satisfied that this was not a cause of, nor a contributory factor to, the explosion.
'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.'
“Instead, there were early signs that a build-up of gas may have been the cause.
'Although there was no gas appliance in use at No. 21, there was a supply - and a meter - which had been unused for some years.
'Preliminary indications are that a large volume of gas may have passed through the meter on May 7, and it is this which has now become the focus of our investigation.'
The body of Emmad Qureshi, 26, was found among the rubble of the neighbouring property. He had died of a wound to the neck caused by falling debris.
A 26-year-old friend of Mr Qureshi, who has not been named, suffered head and arm injuries and is still in hospital where his condition is described as stable.