A man arrested on suspicion of manslaughter over a fatal gas blast may have examined a boiler in one of the affected houses in the days before the disaster.
The 32-year-old, from the Shaw area of Oldham, was held in London yesterday and was being taken to Manchester today for questioning in connection with Tuesday's massive explosion.
Police said they understand the suspect may have done some maintenance work at one of the houses in Buckley Street, Oldham.
Two-year-old Jamie Heaton was killed and neighbour Andrew Partington, 27, suffered serious burns as the blast flattened their homes and damaged scores of other houses.
Jamie was killed while watching TV in his home but his mother miraculously survived after stepping out to hang out washing in the yard.
Local reports suggest there was a problem with the boiler at Mr Partington's home in the days and weeks before the explosion.
Police have also said they are investigating reports of a row involving the injured man and his partner, mother-of-five Tanya Williamson, who left the family home with her children before the blast.
Senior police stressed today that the arrest was only one line of inquiry.
Steve Heywood, Assistant Chief Constable of Greater Manchester Police, said: "A 32-year-old man from the Oldham area was arrested in London and conveyed to Manchester today. He will be subject to a robust interview process today.
"What I would like to stress though is he is just one single line of inquiry we are pursuing. There are a number of other lines of inquiry which we are pursuing.
"I would not want you to read into it that this is actually the only line of inquiry we are pursuing.
"At this stage I would not like to speculate any further around who he is or his occupation because that is going to be a significant part of that particular line of inquiry.
"That is only one line of inquiry. We are treating it as a homicide inquiry, a suspicious death inquiry."
Mr Heywood said police have yet to establish the exact cause of the explosion, and their approach was to "assume nothing, believe no first account and check everything".
He added that officers still have "significant questions" for Mr Partington who remains unconscious and sedated in Wythenshawe Hospital.
He confirmed that recently Mr Partington was arrested and given a conditional discharge in court for common assault following a domestic incident at his home.
A relative of Ms Williamson, who did not wish to be named, said the boiler at the house had developed a problem with the pump around six weeks ago and more recently had a filter changed.
Meanwhile, some residents may never be allowed to return home, according to experts at the scene.
Sean Booth, area manager for Greater Manchester Fire and Rescue Service, said such is the structural damage to some houses that they will have to be demolished, although he could not yet say how many.
Oldham Council said some residents in streets surrounding the epicentre of the blast will begin to return to home this afternoon.
Most, but not all, residents with homes in Oak Street and Gordon Street are to be given access today as the first part of a phased process of return.
Residents can collect items they want to take away or, if they wish, reoccupy their homes - but no utilities are working at present.
Earlier today locals said prayers, lit candles and signed a condolence book for Jamie Heaton at St James's Church, just outside the police cordon.
The Bishop of Middleton, the Rt Rev Mark Davies, said: "More than anything we want to support Jamie's family, for them to know lots of people are praying for them and thinking of them.
"And lighting a candle for Jamie is a powerful symbol in a very dark time for the community.
"The church will give people a place of peace and quiet and a place to reflect.
"There is a very strong community feel here. Although it is quite urban, there is a village feel and this has affected the whole community.
"There is a great outpouring of love, prayer and support for Jamie and his family."
One message in the condolence book read: "Sorry I cannot find the right words for the terrible tragedy.
"May you find help and courage from God to pull you through. Rest in Peace, Little One x."
Darren Webb, a cousin of Kenny Heaton, Jamie's father, laid flowers in tribute to the boy.
Mr Webb said: "It's just awful, distraught. Kenny is a brilliant person, a brilliant dad. They don't deserve this.
"It has been absolute turmoil for all of them."