Investigators in Oregon searching for the person responsible for three fires at ballot drop boxes in the past few weeks – which damaged hundreds of ballots – believe “it is very possible the suspect intends to continue the attacks,” a police spokesperson said Wednesday.

Portland Police Bureau spokesperson Mike Benner described the suspect as a White man between 30 and 40 years old, who is balding or has very short hair. The man has a medium to thin build, he said.

Fires were set at three ballot boxes in the area in the past three weeks. Officials have identified 488 damaged ballots that were retrieved from a burned ballot box in Vancouver, Washington, and 345 of those voters already requested new ballots, according to election officials. Elections staff will mail another 143 replacement ballots to voters Thursday, officials said on X.

An “incendiary device” found attached to the side of a ballot drop box in Portland, Oregon, early Monday damaged ballots, but most were unaffected because of fire suppressant installed in the ballot box.

Police chief Bob Day said the welding on the devices is “very detailed … it’s really quality, so this person obviously has some skills in that area.”

Investigators have not identified the suspect’s name, the chief said. He told reporters they have to presume the suspect will attack again.

“In terms of anticipating future behavior, that’s a speculation,” the chief said. “That’s just what we have to anticipate. It would be really naive of us or unjust for us to say that ‘hey, it’s all taken care of,’ and we don’t have him in custody.”

Security has been stepped up at the approximately 30 ballot boxes throughout Portland, Day said.

Police have said they are looking for a black or dark-colored 2001-2004 Volvo S-60.

Investigators have also linked the two incidents to a third ballot box fire on October 8, also in Vancouver, which is just across the Columbia River from Portland.

Crime Stoppers of Oregon is offering $2,500 for information that leads to an arrest, according to a news release sent Wednesday afternoon by police.

US threat assessment warns of domestic extremist threat to voting infrastructure

While authorities have not announced a suspected motive behind the incidents, they come the same month the US Department of Homeland Security published a threat assessment warning of possible disruptions to the 2024 election.

DHS analysts said domestic extremists “will pose the most significant physical threat to government officials, voters, and elections-related personnel and infrastructure, including polling places, ballot drop box locations, voter registration sites, campaign events, political party offices, and vote counting sites.”

In its assessment, DHS said it had “recently observed a rise in disruptive tactics targeting election officials and offices,” noting the department remained concerned about a possible increase in incidents as Election Day approaches.

Devices found at both scenes Monday and at the ballot box targeted earlier in the month were marked with the words “Free Gaza,” The New York Times reported, citing two law enforcement officials. Investigators are trying to determine whether the suspect is a pro-Palestinian activist or someone trying to sow discord, according to the newspaper.

Officials at Wednesday’s news conference wouldn’t comment on the reports.

All ballot boxes in Multnomah and Clark counties – where Portland and Vancouver are located, respectively – have fire suppressant installed, election officials said at a news conference Monday. Scott said fire suppressant inside the Portland box protected more than 400 ballots inside, and only three ballots were damaged. Election officials said they plan to contact the three voters affected using “unique identifiers on their ballot envelopes, so they can receive replacement ballots.”

Voting in Oregon and Washington is done almost entirely by mail or ballot drop off. Less than 1% of people in Oregon’s Multnomah County vote in person, county Elections Director Tim Scott said. In Clark County, Washington, 60% of the ballots received are from ballot drop boxes and 40% are received by mail, according to Clark County Auditor Greg Kimsey.

On Wednesday, workers searched through the damaged ballots for information in order to contact voters about getting new ones, according to Kimsey. The workers will be able to pull voter information from the ballots despite the damage to them.

This is a developing story and will be updated.

CNN’s Josh Campbell and Taylor Romine contributed to this report.