Oregon Public Broadcasting

Fire investigators are digging in at Marysville Elementary School in southeast Portland.

They're trying to piece together what started the blaze that destroyed about half the building.  As Ryan Knutson reports, it could take a week or more before they're finished.

Investigators used tractors to methodically pull apart the 88-year-old Marysville Elementary School Thursday.

There's no word yet on what started the fire, and Portland Fire Lt. Allen Oswalt says there's also no timeline for when they'll reach a conclusion.

Allen Oswalt: "They’re going to systematically take the rest of the building down in a very controlled manner so they don’t disturb any of the areas that they want to concentrate on."

There are about seven investigators working the case, including some from the Federal Bureau of Alcohol, Tobacco and Firearms. 

Oswalt says federal involvement in a case like this is standard procedure and will help speed up the investigation.

The school’s   students have Thursday and Friday off while school officials prepare Rose City Park Elementary to take them in. That school is about 5 miles away from Marysville.