Pathologists have been brought in from five states to help identify the dead from the Rhode Island concert blaze.
Scores of families are waiting for the worst
As the search for remains ended on Friday the death toll stood at 96 but officials warned that it could still rise as 38 seriously injured patients remained in hospital, 18 of them on ventilators.
So far only 15 bodies have been positively identified and investigators have appealed to relatives of the missing to bring in items such as hair-brushes in the hope of obtaining DNA samples.
Relatives of the missing have been gathering in silence at the Crowne Plaza hotel in West Warwick where Red Cross counsellors, members of the clergy and health officials are mingling with the crowd.
It could be manslaughter, it could be murder, it could be
Rhode Island State Attorney General
"We haven't heard from him since Thursday night," Shelly Gates, aunt of 31-year-old concert-goer Eddie Corbett, said as she clutched a fluffy toy, tears welling up in her eyes.
"We have no further information and now fear the worst."
Forensic experts are using finger-prints, dental records and DNA samples to establish the identity of the dead and their work is expected to take up most of the coming week or longer.
A surgeon at Providence Hospital, Rhode Island, said he hoped that the majority of people seriously injured would survive.
But, William Cioffi added, "these are serious injuries, especially the smoke inhalation".
The state attorney general for Rhode Island has warned that he will bring criminal charges if necessary.
"There could be a whole menu of charges - it could be manslaughter, it could be murder, it could be simple assault," said Patrick Lynch, announcing the start of the investigation.
The attorney general did not give details of where the investigation would be focused.
Teams of police officers are collecting evidence among the charred remains of The Station club and studying a video filmed inside the club as the fire started.
Local TV footage caught the moment the flames took hold
It shows the rock group Great White performing against a backdrop of pyrotechnics.
Great White and the club's owners are in dispute over whether or not permission was given for the pyrotechnic display.
Jack Russell, the heavy metal group's lead singer, said the band's manager had checked with the club before the show that pyrotechnics could be used.
"We had the permission to use the gerbs [stage fireworks]," he said.
"We said: 'This is what we have, this is what it does. Is it OK to use it or not?' If they say yes, no problem. In some places, they say we can't do that, so we don't do it."
But a statement released by lawyers acting for brothers Michael and Jeffrey Derderian who own the club said:
"At no time did either owner have prior knowledge that pyrotechnics were going to be used by the band Great White".
'Way too full'
Rhode Island Governor Donald Carcieri said investigators were examining if the club had been overcrowded on the night.
He said that he estimated that about 350 people had been in a venue designed to hold 300.
Charles Stepinski, who left the club before Great White took the stage, told Reuters news agency that it had been "way too full".
Fans had just minutes to escape the inferno
Thursday night's fire took hold with devastating speed, licking up curtains and foam cladding around the stage as many in the crowd of fans mistook the flames for part of the stage show.
"If you were not out of that building in 30 seconds you didn't have a prayer," Governor Carcieri said.
It was the second nightclub tragedy in the US in less than a week.
At least 21 people were killed in a stampede at a nightclub in Chicago on Sunday night after pepper spray was used to break up a fight.