Maine State Police and the FBI are investigating a threat involving the office of U.S. Sen. Susan Collins and a dozen Maine high schools.

Police have informed all Maine police departments of the threat and the Maine Department of Education has done the same with all Maine school superintendents, according to a statement Friday from Maine Department of Public Safety spokesman Stephen McCausland.

He said the threat was received by a Maine business, which forwarded it to police, and investigators are still trying to identify the source. McCausland would not name the business, nor would he confirm a connection with Collins, a Republican who has been playing a key role in the impeachment trial of President Trump. He also would provide no details about the nature of the threat.

“The threat was made this morning, and we immediately contacted the Capitol Police, who worked closely with the FBI and state and local law enforcement to quickly ensure the safety of Maine schools,” said Annie Clark, a spokeswoman for Collins, in an email.

McCausland would not release the names of the schools involved Friday afternoon but said all are in northern Maine and have “taken appropriate action at the local level” in response to the threat. He said the state police computer crimes unit is also involved in the case.

NewsCenter Maine reported the districts include Bangor, Brewer, East Millinocket, Caribou, Houlton, Madawaska, Jonesport-Beals, Machias and Narraguagus.

Kristen Setera, spokeswoman for the FBI’s Boston division, said in an email that no more information would be released Friday. The bureau was still working with law enforcement to identify the source of the threats, she said.

Jane McCall, assistant superintendent of Caribou-based Regional School Unit 39, said Caribou High School went into a “soft lockdown” mid-morning and expected it to last all day Friday.

A soft lockdown means students still attend classes and move around the school, but there is limited access in and out of the building and there are no outside activities, such as recess or gym classes.

All Maine school districts were advised by the Department of Education Friday to “increase situational awareness, and report any suspicious activity or persons to local law enforcement,” according to a notice shared with the Press Herald by the Brewer School Department.

The notice also asked districts to advise bus drivers to increase their awareness and immediately report suspicious or aggressive behavior by other drivers.

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