The scene at Third and Elm Streets was closed to everyone but investigators Monday. The area is being monitored by security at night.
Fire officials said it's important they get this investigation right because their findings will need to hold up in court if this fire becomes part of a civil or even criminal case.
"A fire always tells a story," said Grand Island Fire Chief Cory Schmidt.
Behind the yellow tape, investigators are trying to read that story.
"Right now it's going pretty slow. We have a lot of debris we have to move," said G.I.F.D. Division Chief Tim Hiemer.
They're doing it by hand, making their way from the least amount of damage to the most, looking for the signs.
"Things melt a certain direction or things burn at different temperatures or smoke leaves a pattern as well as a fire," said Schmidt.
With a fire this large a less common collaboration is going on between G.I.F.D., the State Fire Marshal's Office and private insurance investigators.
"When we lose a structure like this, it really taxes our ability,” said Hiemer. “The city doesn't have the resources. The fire marshal's office doesn't necessarily have the resources."
"If we can get those other agencies involved from the start, it does make it easier on everybody," said Schmidt.
He said insurance investigators often show up when clean-up has started, which hinders their investigation.
Even with the extra eyes, Schmidt said the fire does put a temporary strain on his department.
"Currently we have about four people assigned to the fire here just within our department so it does take away from their normal duties, but we owe it to the community to figure out what exactly caused it," he said.
"We haven't found anything definite yet. We're still ruling out possible causes so it could take a while," said Hiemer.
Fire officials said it could be several weeks before a cause is known.
They'll be bringing in heavy equipment Wednesday to help with the investigation and also hope to get Third Street open.