PORTLAND, Oregon. — The man suspected of setting fire to ballot boxes in Oregon and Washington state was an experienced metalworker and may have been planning additional attacks, authorities said Wednesday.

Portland Police Bureau spokesman Mike Benner said investigators believe the man who installed the incendiary devices at polling stations in Portland, Oregon, and nearby Vancouver, Washington, had “a wealth of experience” in metal fabrication and welding.

Benner said the way the devices are made and attached to metal drop boxes demonstrates this expertise.

Authorities announced that the suspect was a white man, aged 30-40, who was bald or had very short hair.

Police previously said security camera footage showed the man driving a black or dark-colored 2001 to 2004 Volvo S-60. The vehicle did not have a front license plate, but its rear license plate had unknown letters or numbers.

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

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

Investigators are trying to determine the culprit and cause of suspected arson attacks that destroyed or damaged hundreds of ballots at a polling station in Vancouver on Monday, when the fire extinguishing system at the ballot box did not work as intended. Authorities are trying to figure out whether the suspect truly holds pro-Palestinian views or was using the message to create confusion, the official said.

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Surveillance footage captured a Volvo pulling up to a delivery box in Portland just before nearby security personnel noticed a fire inside the box on Monday, Benner said. Police said the fire, which broke out in the early hours of the morning, was quickly extinguished thanks to the box’s extinguishing system and a nearby security guard. Only three of the ballot papers inside were damaged.

Greg Kimsey, the long-time elected auditor in Washington’s Clark County, which includes Vancouver, said there was also a fire extinguishing system inside the burning ballot box in Vancouver, but that system could not prevent hundreds of ballots from burning.

Elections staff were able to identify 488 damaged ballots taken from the drop box, and as of Tuesday evening, 345 of those voters had contacted the county auditor’s office to request a new ballot, the office said in a statement Wednesday. The office will send 143 ballots to the rest of the designated voters on Thursday.

Six of the ballots were not identified, and the office said the exact number of ballots destroyed was unknown because some may have been completely burned to ashes.

On Wednesday, election staff planned to sort through the damaged ballots for information on who cast them, in the hope that those voters could be given new ballots. Kendiy urged voters who dropped their ballots into transit center ballot boxes between 11 a.m. Saturday and early Monday to contact his office for a replacement ballot.

Authorities in Portland said Monday that enough material from the incendiary device had been collected to show that the two fires were linked and that they were linked to an incendiary device used on Oct. 8 that was found at a different trunk in Vancouver. No ballot papers were damaged in this incident.

Voters in Washington are encouraged to check the status of their ballot at: www.votewa.gov To track return status. If the returned ballot is not marked “received,” voters can print a new ballot or visit their local elections department for a new ballot, the secretary of state’s office said.

—Durkin Richer reported from Washington. Gene Johnson in Seattle contributed.