An assembly line worker was charged with vandalizing a military helicopter at Boeing factory, but federal prosecutors said Tuesday that they were still trying to determine who damaged a second helicopter at the plant.

Matthew Kevin Montgomery, 32, of Trevose, was charged with cutting a bundle of wires on an H-47 Chinook helicopter, U.S. Attorney Patrick Meehan said at a news conference. Montgomery was apparently upset about being reassigned to another line at the suburban Philadelphia plant, Meehan said.

The wires were cut the morning of May 10, Montgomery's last day working on the Chinook line at the plant.

"Regardless of what his motivation was, the impact was the same," Meehan said. The helicopter would not have been able to fly with the cut wires, investigators said.

The production line was shut down early last week after the vandalism was discovered by workers inside the Ridley Park plant. Federal officials handed out fliers to workers, offering a $5,000 reward for information in the case.

U.S. Rep. Joe Sestak has said that a suspicious washer was found in the second helicopter. A military criminal investigator described the washer as being in a place it shouldn't have been.

Meehan said authorities were still trying to determine who damaged the second helicopter.

The Chinook is the Army's workhorse aircraft and is used to transport troops and supplies. Boeing is currently producing new Chinooks for the Army, as well as updating older models.

It was not immediately known if Montgomery had an attorney.