Ashway said he was trying to interview as many of the warehouse's 150 day workers and 30 night workers as he can. "I've talked to a lot of them, but I won't be able to talk to all of them," he said.
Pennsylvania State Police Trooper Skip Sydnor, a state fire marshal based in Chambersburg, Pa., is not being called in on the investigation, Ashway said.
He said several inspectors from the insurance company that covers National Book Network's property have been at the scene.
Ashway said he could not say when a cause will be determined.
Officer Bob Wertz of the Washington Township Police Department confirmed Sunday night the status of the investigation was unchanged.
He said company officials have been asking that one be found soon so they can begin to collect damages from the insurance company.
Parts of the 100,000-square-foot warehouse and thousands of books in it were destroyed by fire, smoke and water in the blaze that drew about 40 units from Pennsylvania and Maryland to the scene on National Book Network Road.
The warehouse held millions of dollars worth of hardcover and paperback books, officials have said.
Irving Myers, executive vice president of National Book Network, said Thursday that things were back to normal at the warehouse. "Everybody pitched in and got us back up again," he said.
Nearly all of the thousands of books that were damaged by flames, smoke and water in the fire have been removed, Myers said.
Workers were told not to report to work the day after the fire. They returned Aug. 14 and by the end of the day the warehouse was back to about 75 percent of its capacity, Myers said. "By Friday we were back up to 100 percent."
"Most people who come in here today would not know there was a fire," he said.
Myers had no damage estimate as of Thursday.