Vandals have again broken into a high school under construction in the western end of Prince William County, causing $70,000 worth of damage and cleanup costs, county police reported last week.

County police spokesman Dennis Mangan said that 13 fire extinguishers were discharged in the halls of Battlefield High School, 15000 Graduation Dr., near Haymarket, early on June 5. Paint thinner was poured on the basketball court, and light fixtures and door handles were damaged. The vandalism occurred between 1:30 a.m. and 6 a.m.

The vandals got into the school through a door that was damaged in an earlier vandalism incident, Mangan said. On May 3, someone broke the glass on a door, reached in and opened it. Afterward, the hole in the door was covered with a piece of fiberboard, which was punched out to gain access during the most recent incident, Mangan said.

In addition, vandalism was reported at the school April 30, and the contractor, Dustin Construction of Gaithersburg, filed a theft report March 23, Mangan said.

Such incidents are common at construction sites, when workers leave valuable items unsecured and doors unlocked, Mangan said.

Daniel A. Dustin, executive vice president for Dustin Construction, did not return calls seeking comment Friday. The school is still the property of the construction company until work is complete. Battlefield High is scheduled to open this year.

Principal Jack Parker said the most costly part of the incident was the cleanup. The fine powder in the fire extinguishers had to be cleaned up using special equipment and removed from the ventilation system. The paint thinner might have been spilled by workers and not vandals, Parker said.

The cleanup is complete, and the contractor's insurance company should handle the costs, Parker said.

"By Tuesday, you wouldn't know anything had happened," Parker said. Security cameras are about to be installed and a security resident, who will live full time at the school site, is moving in soon.

Police ask that anyone with information about the incident call Crime Solvers at 800-673-2777. Callers do not have to give their names, and Crime Solvers pays rewards of up to $1,000 for information that leads to arrest and indictment.