By ALANNA DURKIN RICHER and CLAIRE RUSH

PORTLAND, Ore. (AP) – The man suspected of setting fire to ballot boxes from Oregon and Washington state is an experienced metal worker and may be planning other attacks, authorities said Wednesday.

Investigators believe the man who planted the incendiary devices at ballot boxes in Portland, Ore., and nearby Vancouver, Wash., had “extensive experience” in metal fabrication and welding, Portland Police Bureau spokesman Mike Benner.

The way the devices were constructed and the way they were attached to the metal delivery boxes showed that expertise, Benner said.

Authorities described the suspect as a white man, between 30 and 40 years old, who is bald or has very short hair.

Police previously said surveillance video was presented the man driving a black or tan Volvo S-60 from 2001 to 2004. The vehicle had no front license plate but had a rear plate with unknown letters or numbers.

The incendiary devices were marked with the message “Free Gaza,” according to a police official who spoke to The Associated Press on condition of anonymity because they were not authorized to discuss an ongoing investigation.

A third device placed in a different drop box in Vancouver earlier this month also bore the words “Free Palestine” in addition to “Free Gaza,” the official said.

Investigators are trying to identify the person responsible and the motive for the alleged arson attacks, which destroyed or damaged hundreds of ballots at the box office in Vancouver on Monday when the box office’s fire suppression system failed to operate as intended. Authorities are trying to determine whether the suspect actually held pro-Palestinian views or used the message to try to create confusion, according to the official.

Surveillance footage captured a Volvo pulling up to a storage box in Portland just before nearby security personnel discovered a fire inside the box on Monday, according to Benner. The early morning fire was quickly extinguished thanks to the box’s suppression system and a nearby security guard, police said. Only three of the ballots inside were damaged.

The Vancouver ballot box that burned also had a fire suppression system inside, but it failed to prevent hundreds of ballots from burning, said Greg Kimsey, the longtime elected auditor of Clark County, Wash., who also includes Vancouver. Kimsey said Tuesday that the exact number of ballots destroyed was not known and that about 475 damaged ballots were retrieved from the box.