A 35-year-old woman was on Wednesday sentenced to 18 years in prison for sending poisonous ricin-laced letters to US President Barack Obama and former New York Mayor Michael Bloomberg.
Shannon Guess Richardson from Texas was sentenced on a charge of possessing and producing a biological toxin.
She had pleaded guilty to the charge in December in a deal.
She was named in an indictment returned by a federal grand jury on June 27, 2013, charging her with threatening the US President, Bloomberg and Mark Glaze, who was director of Bloomberg's group advocating for tougher gun control.
Richardson was sentenced to 216 months in prison by US District Judge Michael H Schneider and ordered to pay restitution in the amount of $367,222.29.
According to federal prosecutors, during April-May 2013, Richardson made several online purchases of items for the purpose of producing ricin.
Ricin is a biological toxin that can be fatal if ingested, inhaled, or injected. There is no known antidote or cure for ricin poisoning.
Richardson subsequently placed ricin onto threat letters addressed to Obama, Bloomberg and Glaze.
On May 20, 2013, Richardson mailed the three threatening letters from the New Boston, Texas, Post Office.
On May 30, 2013, Richardson travelled to the Shreveport, Louisiana, and reported that her husband was responsible for the ricin-laced letters.
Richardson was arrested on June 7 last year and has been detained since that time.