The house in Omagh in which a family is believed to have died in a fire is now a "potential crime scene", according to police.
The McElhill family lived in the end-terraced house
Detectives said they had not ruled out arson. It follows the removal of a number of items for examination.
A senior fire investigator is also being flown in from England to assist with the investigation.
Arthur McElhill, Lorraine McGovern and their five children are thought to have been killed in Tuesday's blaze.
When asked if he was considering the possibility of arson, Chief Superintendent Norman Baxter - the police officer investigating the fire - said police are not ruling anything out.
He added that the bodies of the McElhill family would not yet be taken from the house.
Five bodies have been found in the house at Lammy Crescent. The search is resuming for the remaining two members of the family of seven.
On Wednesday, Fire Service Western Area Commander Eoin Doyle said the priority was finding the two people "not yet accounted for".
He said that additional firefighters were being drafted in to help find the bodies and establish how the fire began, just before 0500 GMT on Tuesday.
Prayers were said for the family during a church service
"We've had the ceilings fall down on top of the belongings and a partial roof collapse, it's going to make it a very slow process for us," he said.
Mr Doyle said that it had been a "harrowing experience" for the local firefighters and trauma support for the crews had begun.
Father Tom McManus, the parish priest in Corlough in County Cavan where Lorraine McGovern grew up, said they had been a very close family.
"It's just devastating when you look back at those things, the happy times and the good times," he said.
"They were reminiscing about that the last time we had spoken together - the last time they had visited, at the baptism... it's just horrendous."
The eldest of the five children, Caroline, 13, attended the nearby Sacred Heart College.
The other four were Sean, 7, Bellina, 4, Clodagh ,19 months and James, who was nine months old.
Sean and Bellina were pupils at St Conor's Primary School, which was closed following the tragedy.