(Vancouver, WA) -- Investigators say it will likely be a few days before they determine what caused a fire that destroyed an old pine cone factory in Vancouver. Police are searching for three "persons of interest" in the case, believed to be around 16- or 17-years-old. Witnesses say they saw at least one of the youths carrying what appeared to be a gasoline canister. The fire broke out Friday at the Northeast 28th Street property, which had been sold to a California buyer who planned to develop it into apartments.