Investigators sifting through the charred rubble include the Houston Fire Department's arson division the Texas Rangers, the State Fire Marshall's Office, A.T.F and HPD's homicide division.
Currently very little information is being released.
Officials won't say if the four firefighters that died were told someone was trapped in the burning building.
"They entered the building as a matter of protocol," said Houston Fire Captain Ruy Lozano. "When you have a commercial structure during normal business hours which this was there's the need for a primary search to ensure everyone is out."
Anyone with information about the fire is urged to call HFD's arson division but officials say nothing should be read into that plea regarding the cause,
The restaurant where the fire apparently originated had been inspected by the fire department but no violations were found.
The city's health department found several violations in the last 2 years but there's nothing unusual about those violations.
The four deaths in the line of duty coupled with the number of agencies involved means the investigation could take months.
"Absolutely I can see this taking months before we get a clear formal account of what happened," Lozano said.
Meanwhile houstonians are still placing flowers and balloons at fire stations 51 and 68.
It was something this woman said she had to do because of what station 68 did for her.
"I know they saved my life one time and that's why I'm here," the unidentified woman said. "I almost drowned and this fire station helped me out."