Story highlights Shannon Richardson, 35, initially told FBI her husband sent ricin-tainted letters

But she failed polygraph, and husband said she wanted to end marriage, FBI says

Before her arrest, she allegedly admits to mailing letters, but says husband forced her

Her husband files for divorce; she's also pregnant, divorce lawsuit says

A Texas actress in a troubled marriage was arrested and charged Friday in connection with ricin -tainted letters that were mailed last month to President Barack Obama and New York City Mayor Michael Bloomberg, authorities said.

Shannon Richardson, 35, also known as Shannon Rogers and Shannon Guess, initially told the FBI that her husband, Nathaniel, sent the ricin-laced letters, but a polygraph exam found her to be "deceptive" on the matter, court papers said.

Investigators found that her computer storage devices contained the text of threatening letters sent to the president, but the couple's computer records show her husband couldn't have printed them out because he was at work at the time, an FBI arrest affidavit said.

On Thursday, Shannon Richardson told investigators she mailed the ricin-tainted letters, but she claimed that her husband typed the letters and forced her to print and mail them, the affidavit said.

Her husband denied involvement and claimed his wife wanted to end their marriage and leave him, the affidavit said. He told investigators that his wife was "intentionally misleading" them, the court papers said.

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Shannon Richardson is accused of mailing a threatening communication to the president and faces up to 10 years in prison if convicted, according to a statement from U.S. Attorney John M. Bales' office in Texas.

Also on Thursday, Nathaniel Richardson filed for divorce. His wife is pregnant, and the anticipated birth date and sex of the fetus is not known, the divorce lawsuit said. The couple married on October 8, 2011, the suit said.

Shannon Richardson allegedly also mailed a third letter with the toxin ricin to Mark Glaze, director of Mayors Against Illegal Guns, which was founded and co-chaired by Bloomberg, the FBI arrest affidavit said. The group's office is in Washington.

She made an initial appearance Friday afternoon before U.S. Magistrate Judge Caroline Craven in Texarkana, Texas, the prosecutor said. She was arrested in Mount Pleasant, Texas, authorities said.

The three letters were mailed from Shreveport, Louisiana, last month, federal authorities say.

The FBI found "very low concentrations" of ricin on the letters, a spokesman said last month.

Richardson has had minor roles in TV series, including "The Walking Dead" and "The Vampire Diaries."

A law enforcement official told CNN that investigators believe Richardson sent the letters herself. She was angry at her husband, the official said.

CNN reported early in the investigation that the FBI considered Richardson to have serious credibility issues when they began interviewing her.