BOULDER COUNTY, Colo. (KDVR) — Nearly a month after the Marshall Fire, so many questions remain about the most destructive fire in Colorado history. Near the top of the list: What started it? And where?

“It could take months. It could literally take months,” said Tony Satriano, a fire investigator for West Metro Fire Rescue for more than 40 years. He declined to speak specifically about the Marshall Fire, but he did offer insight into what exactly investigators are looking at.

This week, the Boulder County Sheriff’s Office narrowed its list of likely potential causes to downed power lines, human activity and underground coal mines in the area.

“We go from the large picture, the biggest picture that we see showing up, and we narrow it down,” Satriano said.

He said one of the first steps is determining how exactly the fire spread, and then figuring out a general area for the ignition. Investigators appear to have done that already, focusing on an area south of Boulder near Highway 93 and Marshall Road. 

Satriano said investigators will interview the first firefighters who were in the area to try and narrow that location down even further.

“What did you see? What did you feel?” he said they’ll ask.

He said cell phone videos are also extremely helpful, allowing firefighters to visually see areas where the blaze may have started.

“Video is all around us, it’s every day, and we use it to our advantage, we really do,” he said. “That’s like us showing on scene right with the fire crews. It’s amazing because you can see the intensity, the volume, the smoke.”

Satriano said it’s a tedious process, but one that’s critical to the community. At stake are hundreds of millions of dollars in insurance claims, and potentially, criminal charges.

“What we do goes hand in hand with the product liability, as well as with the insurance industry,” he said. “We have to find the truth in every incident.”