PORTLAND, Oregon. — the man suspected of setting fires in electoral boxes in Oregon and Washington state is an experienced metal worker and may be planning additional attacks, authorities said Wednesday.

Investigators believe the man who placed the incendiary devices in ballot boxes in Portland, Oregon, and nearby Vancouver, Washington, had “extensive experience” in metal fabrication and welding, a Portland Police Bureau spokesman said. Mike Benner.

The way the devices were built and the way they were attached to the metal mailboxes demonstrated that expertise, Benner said.

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

Police previously said surveillance video showed the man driving a Volvo S-60 black or dark color 2001 to 2004. The vehicle did not have a front license plate, but it did have a rear license plate with unknown letters or numbers.

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The incendiary devices were marked with the message “Free Gaza”, according to a law enforcement 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 mailbox 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 a Vancouver mailbox on Monday when the mailbox’s fire suppression system failed to function as intended. Authorities are trying to determine whether the suspect actually held pro-Palestinian views or used the message to try to create confusion, the official said.

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

The ballot box that burned in Vancouver also had a fire suppression system inside, but it failed to prevent hundreds of ballots from being burned, said Greg Kimsey, a longtime elected auditor in Clark County, Washington, which includes Vancouver.

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Election staff were able to identify 488 damaged ballots recovered from the ballot box, and as of Tuesday night, 345 of those voters had contacted the county auditor’s office to request a replacement ballot, the office said in a statement Wednesday. The office will mail 143 ballots to the rest of the identified voters on Thursday.

Six of the ballots were unidentifiable and the office said the exact number of ballots destroyed was not known, as some may have been completely burned to ashes.

On Wednesday, election staff planned to sort through damaged ballots to obtain information about who cast them, in hopes those voters can receive replacement ballots. Kimsey urged voters who dropped their ballots in the transit center drop box between 11 a.m. Saturday and early Monday morning to contact his office for a replacement ballot.

Portland authorities said Monday that enough material was recovered from the incendiary devices to show that the two fires were connected, and that they were connected to an Oct. 8 incendiary device at a different voting booth in Vancouver. No ballots were damaged in that incident.

RELATED |Washington voters have already returned more than 1.75 million votes.

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