Criminal investigators from the Defense Department yesterday offered a $5,000 reward for information leading to the conviction of those responsible for damaging two Army helicopters at the Boeing Co. plant in Delaware County.

The production line for the CH-47F Chinook had been shut down since Tuesday, when the defects were discovered, but employees returned to work yesterday.

Army spokesman Dave Foster said yesterday that the damage to the twin-engine helicopters "has been determined to be an isolated incident" but that the investigation would continue.

Severed wires were found in one Chinook and a misplaced washer in another, according to U.S. Rep. Joe Sestak, a former Navy admiral whose district includes a portion of the sprawling rotorcraft plant in Ridley Township.

Federal officials yesterday were handing out fliers to workers, offering a $5,000 reward for information about the "vandalism" of the two nearly completed aircraft.

"We have determined that this was a deliberate act and not an accident," said Ken Maupin of the Defense Criminal Investigative Service. He said 10 DCIS agents have been assigned to the case.

"There are federal statutes that would implicate anybody who intentionally interfered with a mechanism like this that is being introduced into a theater of war," U.S. Attorney Pat Meehan said.

Anyone with information about the case is asked to call DCIS at 267-228-2782.

The Associated Press contributed to this report.