ANCHORAGE — An Alaska man faces federal charges after authorities allege he threatened to hire an assassin to kill U.S. Sen. Lisa Murkowski, according to court documents unsealed Wednesday.

In a separate threat left in a voice message at Murkowski’s Washington, D.C., office, the caller asked if the Alaska Republican knew what a .50 caliber shell does to a human head, according to court records unsealed Wednesday.

Jay Allen Johnson, 65, of Delta Junction, was scheduled to make his first appearance in U.S. District Court in Fairbanks on Wednesday over allegedly making threats against two senators but the hearing was continued until Thursday, the U.S. Attorney’s Office said.

The two senators were not named by the U.S. Attorney’s office or in an affidavit outlining the investigation filed by Matthew Patrick Allen Oudbier, an FBI special agent.

However, Karina Borger, a spokesperson for U.S. Sen. Lisa Murkowski, confirmed in an email to The Associated Press that the Alaska Republican was one of the targets and was listed in the affidavit as “Senator 1.”

“Threats should be taken seriously and our laws should be enforced to ensure accountability,” Borger said in a follow-up email to the AP. “Senator Murkowski is thankful for the hard work of the federal law enforcement and for all they do to keep us safe.”

Alaska’s other U.S. senator, Dan Sullivan, was “Senator 2” in the affidavit, his senior adviser Amanda Coyne said in an email. Sullivan would have no further comment since this is an ongoing investigation, she said.

Johnson was arrested Monday and was being held at the Fairbanks Correctional Complex. Gary Colbath, a federal public defender, has been assigned the case and didn’t immediately return a phone message to the AP seeking comment. Charging documents in the cases were filed Oct. 1 under seal, which was lifted Wednesday.

Johnson faces several charges, including threatening to murder a U.S. official with intent to intimidate or impede that person while conducting their official duties, making interstate threats and threatening to damage property by fire or explosives, according to a criminal complaint filed in federal court. No motives were detailed in the affidavit.

The phone system at the senators’ offices captures the caller ID of incoming calls. An investigation into the number led law enforcement to a woman identified only by the initials “CP” who married Johnson in Texas in 2016, the affidavit said. Further investigation matched the number to both Johnson and CP, and both to a post office box and a redacted physical address in Delta Junction, the court documents say.

Delta Junction, a community of just under 1,000 residents, is located about 100 miles southeast of Fairbanks.

In the affidavit, the last four digits of the telephone number are redacted but the area code and first three digits of the phone number are the same and used in all the calls, the affidavit says.

In the affidavit, the senators are only referred to by the numbers 1 and 2.

It states that on Sept. 29, a voice message left at the office of Senator 1, or Murkowski, was directed to the senator by name and the caller threatens to hire an assassin. The message said, “resign or get the f—- gone, or die,” according to the affidavit.

Another voicemail had been left at Murkowski’s office on Sept. 2. The caller said: “I will find out everything, where you’re at. I will find out all of your properties and I will burn everything you hope to have, and I will burn everything you hope to own.”

The caller then says he’ll use his skills as a veteran: “50 caliber shell, you ever see what that does to a f——- human head?”

Officials say Murkowski’s office also received four other voicemails from the same telephone number between August and September.

The affidavit also says Senator 2 received 13 voice messages between April to September, and in several the caller identified himself as Jay Johnson. In another, the caller gave that name along with an address in Delta Junction, the court documents say. No details of those calls were released.