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Man arrested over threats to kill senator

*** UPDATED 3:10 PM ET ***

From NBC's Pete Williams
Federal prosecutors have charged a Washington state man, Charles Alan Wilson, with repeatedly making threatening calls to Sen. Patty Murray's Seattle office, threatening to kill her because of her support for the health care bill.

FBI agents say they arrested Wilson after getting telephone records and calling him to confirm that his voice matched the one left on voicemail in Murray's office.

The investigation began in late March, after the health-care bill was passed, when a staff member notified the FBI that a man, who had been calling the Seattle office for months, leaving messages after hours, had begun making overt threats to kill her.

In one message, according to court documents, he said, "I hope you realize, there's a target on your back now. There are many people out there who want you dead. ... Kill the ----ing senator.  I'll donate the lead." In another, he describes himself as "a senior citizen on Social Security and Medicare" and says, "I want to thank you so much, very, very much, for signing my death warrant."

FBI agents checked the office phone records against the times the voicemails were received, leading to Wilson's number in Selah, Wash. As an additional check, an agent posing as a volunteer from a fictitious group opposed to the bill, called Patients United Now, called Wilson on April 1st and talked to him for 14 minutes. He said he "hated" the law and that he had repeatedly called Murray's office to complain, referring to her with a phrase, "Sneaker Shoes Murray," also often used on the voicemails.

The FBI also determined that Wilson has a handgun registered to him and a valid concealed-weapons permit.

He's charged with threatening a federal official, a felony carrying a maximum penalty of 10 years in prison.