An incendiary device placed in ballot boxes in Portland, Oregon and Vancouver, Washington this month reportedly contained written messages in support of Gaza and Palestine.
The first incident occurred in Vancouver on Oct. 8, in which a device was placed in a drop box with the phrases "Free Palestine" and "Free Gaza" written on them.
Then early Monday, two more ballot boxes – one in Portland and another in Vancouver – were set alight with incendiary devices marked with the message "Free Gaza."
A law enforcement official confirmed the "Free Gaza" and "Free Palestine" messages to The Associated Press, speaking on the condition of anonymity. Both the Portland and Vancouver Police Departments would not confirm the messages, directing questions to the FBI.
FBI Portland has said it is actively investigating both situations.
Police said the incendiary devices were placed on the outside of the boxes.
All three incidents are believed to be connected. Authorities said Wednesday that the man suspected of setting the drop boxes on fire is an experienced metalworker and may be planning additional attacks.
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Authorities describe the suspect as a white man, aged 30 to 40, who is balding and has very short hair.
Police previously said surveillance video 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 it did have a rear plate with unknown letters or numbers.
No ballots were damaged in the Oct. 8 incident. Only three ballots were damaged in the arson in Portland, but hundreds were damaged in the attack in Vancouver.
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Greg Kimsey, the elected auditor in Clark County, Washington, said the exact number of ballots destroyed in Vancouver isn’t known at this time, but officials retrieved about 475 damaged ballots from the box.
Kimsey has called the arsons a "direct attack on democracy."
Kimsey said police will increase patrols around ballot drop box locations and Clark County Elections Office employees will observe ballot boxes 24 hours a day, seven days a week until the election is over.
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Election staff on Wednesday planned to sort through the damaged ballots for information about who cast them, in the hopes that those voters can be given replacement ballots.
Fox News Digital's Stepheny Price contributed to this report.