Officials have closed the case on Winthrop University's Owens Hall fire without knowing what caused the March 6 blaze.
Rock Hill fire officials ruled the cause of the fire at the three-story, $6.2 million building as undetermined.
"We have no other evidence left to investigate," said Rock Hill fire Capt. Otis Driggers. "We've looked at everything that we can. Sometimes you have cases with a lot of destruction like this and you can't identify an ignition source."
Driggers said that leads to an undetermined cause, which means there's nothing investigators can pinpoint as what started the fire.
"Unfortunately, you have those times that you can't identify cause of the fire," he said.
University officials said it will take $4.5 million to restore the classroom building, which opened in 2007 and now must undergo a near-total interior renovation that would include new furniture and new wiring.
Fire officials said the blaze, which burned for about 24 hours, started on a small section of flat roof where Owens Hall and Bancroft Annex connect.
The area where the fire started was secured, Driggers said. "No one had access to the area."
He said it was unlikely anything could have been thrown near that area.
The only mechanical equipment on the roof is an exhaust fan, which Driggers said was ruled out as a cause. He said there also were some roofing materials being stored there by a contractor working on nearby buildings.
While the contractors did have access to the area, Driggers said, no one was working on the day of the fire, a Saturday. He said there were representatives from the roofing company working Friday.
Officials also reviewed and ruled out the mechanical room, HVAC and elevator systems.
Restoration work on Owens Hall continues, and Winthrop spokeswoman Rebecca Masters said the roof decking has been replaced to keep the building dry. Workers are about halfway finished with replacing roof shingles.
Inside, orders are being placed for replacement tiles, Sheetrock, technology and fixtures, Masters said. The building, which houses 18 classrooms, a computer lab, two conference rooms and a student lounge, probably won't be restored in time for class this fall, Winthrop officials have said.