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 and was due to be questioned in Manchester 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 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.
"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."
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".