Shannon Richardson, the actress who admitted sending toxin-laced letters to President Barack Obama last year, was sentenced Wednesday in a U.S. federal court in Texas to 18 years in jail.

The actress, 36, was also ordered to pay US$367,000 in restitution, according to the U.S. Attorney's office.

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John Bales, U.S. attorney for the Texas eastern district, said the sentence brings a fitting end to what has been "surely one of the most unusual, even bizarre cases" in U.S. criminal history.

Richardson had also sent letters laced with ricin, a highly toxic compound derived from castor beans, to then-mayor Michael Bloomberg of New York City, and to Mark Glaze, when he was sitting as director of Mayors Against Illegal Guns, which Bloomberg founded.

The letter to Obama read, "What's in this letter is nothing compared to what ive (sic) got in store for you mr (sic) president. You will have to kill me and my family before you get my guns. Anyone wants to come to my house will get shot in the face."

The actress, who had minor roles in "The Walking Dead" and "The Vampire Diaries," pleaded guilty last December to possession of a toxin for use as a weapon.

The charge carried a maximum penalty of life in prison, but the plea deal said Richardson would not serve more than 18 years.

The ricin-laced letters were sent to Obama and Bloomberg from Shreveport, Louisiana in May 2013, after the actress made online purchases of castor beans and lye, as shown by prosecution records.

Richardson lived in New Boston, Texas, some 90 miles north of Shreveport.

The letters were discovered  before causing any injuries or fatalities. The FBI said they contained very low concentrations of the toxin.

Richardson had told FBI agents that it was her now-estranged husband that had sent the letters, but later changed her story and said she did mail the letters, but it was her husband who typed them and forced her to print them out and mail them.

Nathaniel Richardson testified in court and said Shannon was "intentionally misleading"  investigators.

Nathaniel filed for divorce in June 2013.

TagsShannon Richardson, Barack Obama, Michael Bloombeg, toxic letter to obama