SEATTLE — Police said Monday that a “suspect vehicle” has been identified in connection with incendiary devices that set fires to ballot drop boxes in Oregon and Washington state.

Surveillance images captured a Volvo stopping at a drop box in Portland, Oregon, just before security personnel nearby discovered a fire inside the box Monday, Portland Police Bureau spokesman Mike Benner told a news conference.

That fire damaged three ballots inside, while officials say a fire at a drop box in nearby Vancouver, Washington, early Monday destroyed hundreds of ballots. The devices were attached to the outside of the boxes, police said.

Authorities said at a news conference in Portland that enough material from the incendiary devices was recovered to show that the two fires are connected — and that they were connected to an incident Oct. 8, when an incendiary device was placed at a different ballot drop box in Vancouver.

The ballot drop boxes in Washington and Oregon have fire suppression systems that are designed to activate when the temperature inside reaches a certain point, coating ballots inside with a fire-suppressing powder.

The system appeared to have worked in the Portland drop box, and security staffers were nearby to help put out the fire. Multnomah County Elections Director Tim Scott said the county has contracted with private security officers to have “roving patrols” that operate 24 hours a day and “put eyes” on all drop boxes.

For unknown reasons, the system failed to activate for the ballot box in Vancouver, just across the Columbia River from Portland.