DENVER — Two days after a fire ravaged an apartment building under construction in Denver, the investigation into what sparked the blaze continues.

On Friday, dozens of investigators, including agents with the federal Department of Alcohol, Tobacco and Firearms, combed through what was left of the building near East 18th Avenue and Emerson Street.

Officials still have not said what started the fire that killed two construction workers and injured at least six other people, including a firefighter.

Meanwhile, people who live and work in the buildings nearby are still unable to return.

Some said they’ll have to wait for the power to return and for an inspection to make sure their homes and businesses are safe.

Xcel Energy crews spent hours tearing down burned-up power poles and replacing them and downed wires.

They used a portable crane to move two of the burned vehicles in a parking lot to the west side of the building.

On Friday morning, more than a dozen construction workers from organized carpenter groups gathered in the shadows of the building.

They’re concerned about what they call potentially dangerous working conditions at construction sites.

“What has happened here is unacceptable,” said Mark Thompson with Colorado Carpenters. “People need to be held accountable. … Who is responsible and how could this have been avoided.”

People who live and work nearby will be able to spend time in their homes and businesses temporarily on Saturday and Sunday from 7 a.m. to 7 p.m.