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Laura Seitz, Deseret News
Members of the Bureau of Alcohol, Tobacco, Firearms and Explosives investigate the scene of Sunday evening's fire on 500 South in Salt Lake City on Wednesday, Feb. 12, 2014. The 4-alarm fire caused $2.5 million in damage to the four-story building, which was still under construction when it caught fire.

SALT LAKE CITY — Investigators will return to the site of Sunday's four-alarm fire Thursday, continuing the search for what started the massive blaze.

A team of federal investigators from the Denver office of the Bureau of Alcohol, Tobacco, Firearms and Explosives joined the Salt Lake City Fire Department to search the wreckage of the fire, which caused an estimated $2.5 million in damage to a future apartment building at 540 E. 500 South on Sunday evening.

Following the team's evening briefing Wednesday, Salt Lake City fire spokesman Jasen Asay said investigators would be back on the scene the next morning.

"It's a day-by-day thing," Asay said. "Just like with any investigation, it could be over fairly quickly, or it could last another week or so."

Meanwhile, 500 South will remain closed between 500 East and 600 East while investigators work, he said.

This is the first time ATF has been called in to investigate a fire in Salt Lake City, Asay said. The team was called in because of the size of the fire and not necessarily because arson is suspected.

Investigators will not determine whether the fire could be arson until a cause has been identified, Asay said.

Should foul play be suspected in the fire, the ATF team will provide interviewers to talk to potential suspects, Asay said.

Sunday's fire decimated the building under construction, which would have been a 64,000-square-foot apartment building, and prompted evacuations of nearby homes and a Smith's Marketplace across the street.

The construction company working on the building, U.S. Development, told fire officials that no one was in the building when the fire started. No workers were on site Sunday, and there was no power connected to the building or heat sources inside.

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