A 13-year-old boy admitted to police that he started a two-alarm fire at a vacant Marysville sawmill on July 23, said Cmdr. Robb Lamoureux of the Marysville Police Department.

The boy went to the police station Monday, along with his parents, and said he was responsible for starting the fire at Welco Lumber Yard.

On the day of the fire, witnesses told police they had seen a group of juveniles in the area just before the fire started, Lamoureux said.

Three other Marysville boys, all 13, have also been identified as being with the suspect at the time of the fire, but are being treated as witnesses, Lamoureux said.

The boy was released to the custody of his parents.

Arson investigators are expected to file the case with the Snohomish County Prosecutors Office.

The roof on part of the mill collapsed during the blaze. No injuries were reported.

Damages to the building are estimated at $100,000; however, there are no plans to rebuild at the site. Clean-up of the site is estimated to be $15,000.