A team of federal investigators has joined local and state agencies at the site where the historic Younkers Building once stood.
Officials say they still can't rule anything in or out.
Today's high winds are keeping the team of highly specialized fire investigators from ATF from getting too close to the burned out building.
While they wait for the debris to settle, investigators are interviewing witnesses including the last people to step foot inside the building.
Des Moines firefighters first on the scene Saturday morning were faced with the top two floors on fire and glass falling.
Six firefighters dodged the falling debris as they ran into the building.
“You could probably almost say the building shook a little bit and it sounded like a jet engine,” Des Moines firefighter Travis Hurley describes.
Moments later, the 12-year veteran learned that the roof had caved in.
As fire officials radioed in for them to get out, Hurley waited for the rest of his team to make their way down from the fourth floor.
“They didn't immediately respond so again you have that brief thought of ‘did they get caught in this or not?’” Hurley says.
Just as he was about to run upstairs, they rounded the corner and all six managed to escape before the eight story structure collapsed.
The unstable conditions in and around the fire scene are making the investigation a painstaking process.
“There's still debris falling down from the buildings around the scene. There's also debris lifting up from inside the scene,” ATF’s John Ham says.
The ATF’s National Response Team is working behind the scenes to piece together what sparked the fire.
“Our experts are up in the buildings looking down at the fire scene because that gives them unique perspective to see different components of the fire and perhaps how it burned,” Ham adds.
The firefighters inside the building Saturday morning return to duty Monday after an eventful weekend.
“It makes me proud to be able to say that I’m a Des Moines firefighter,” Hurley adds.
ATF expects to be on scene for the next week helping the Des Moines Fire Department and the state Fire Marshal's Office in the investigation.
It's the first time the team of experts has been called in to help in Des Moines.