A Vancouver, Wash., man accused of sending letters containing white powder to members of Congress fell under FBI scrutiny after his wife told an officer that he laced the envelopes with a mixture of celery salt and corn starch.

The FBI focused on Christopher Lee Carlson, 39, after a Vancouver police officer told them about a March 4 interview she had with Carlson's wife about Carlson's recent emotional turmoil, The Oregonian reported (http://is.gd/EzrAUI).

On March 9, a federal grand jury in Portland, Ore., indicted Carlson on charges that he mailed threatening letters to Republican House Speaker John Boehner of Ohio and Democratic Sen. Barbara Mikulski of Maryland.

The two counts arose from an investigation into the mailing of about 100 envelopes containing white powder. The U.S. attorney's office in Portland said the letters, postmarked in Portland, have tested negative for toxic substances.

Carlson, a nurse, is expected to be arraigned this week.

Investigators have recovered dozens of letters addressed to U.S. senators and representatives. The Seattle office of Sen. Patty Murray, D-Wash., said it also received one of the letters.

Some letters were sent to Congress members' district offices.

The letters, which first came to light in late February, told the recipients that there is a "10 percent chance you have just been exposed to a lethal pathogen."

The sender wanted an "end to corporate money and `lobbying,'" an end to corporate "personhood" and a new constitutional convention. The Associated Press obtained a copy of a letter.

The Oregonian reported Carlson earned a nursing degree and went to work at Legacy Salmon Creek Medical Center in Vancouver in November 2008. He worked there until July 2010, when he started teaching other nurses how to use Legacy Health's electronic medical records system, said Brian Terrett, Legacy's chief spokesman.

Carlson took a leave of absence in December and, according to a Vancouver police report, admitted himself to a Portland psychiatric center as suicidal. On Dec. 14, an officer removed four guns and boxes of ammunition from the apartment he shared with his wife, police said. On Jan. 23, another officer said he found Carlson barricaded inside the apartment.

Vancouver police Officer Leah Supriano was on patrol March 4 when a dispatcher reported concerns about possible domestic violence at the Carlson home. Supriano phoned Adrienne Carlson, who said her husband had verbally abused her and left. Then she gave the officer a statement about suspicions her husband had committed a crime.

"Adrienne told me that a few months ago, Chris had talked about sending letters to members of the Senate and the media to express his frustration with certain things," Supriano reported. "About two weeks ago, they were driving in Portland ... and when they passed a post office somewhere off Stark (Street), he pointed at the post office and told her that he was worried and wondered if they had surveillance cameras."

"Oh no, you didn't send those letters did you?" Adrienne Carlson said, according to the report.

Christopher Carlson acknowledged that he did, his wife reported.

The letters bore a return address from "The MIB." According to the police report, Adrienne Carlson told the officer "MIB" meant "Man in Black." She also said her husband told her he had filled the envelopes with a mixture of celery salt and corn starch. She added he was planning to send a second round of letters that would contain lye, a highly corrosive chemical used to make soap and detergents.

The listed Portland return address didn't exist.

Vancouver police forwarded the woman's suspicions to the FBI, which investigated in conjunction with the U.S. Postal Inspection Service and U.S. Capitol Police.

Carlson's mother, Rose Hatch, and his stepfather, Bryce Hatch, described him as extremely bright, The Oregonian reported. But they said he had a somewhat contemptuous view of politicians and was disappointed that President Obama had not lived up to his high expectations.

Carlson appeared briefly Monday in federal court in Tacoma, Wash., since he was arrested in Washington state. He agreed to be moved from a Washington state detention center to a Portland jail. It wasn't known if he was represented by a lawyer.