An actress who has appeared in Tv hits The Walking Dead and The Vampire Diaries has been sentenced to 18 years behind bars for sending ricin-laced letters to U.S. President Barack Obama and former New York Mayor Michael Bloomberg.

Shannon Rogers Richardson pleaded guilty to the crime in December (13), six months after she was arrested for sending three 'poisoned' notes to Obama, Bloomberg and his colleague Mark Glaze, threatening harm if they continued to push for tougher gun control laws.

The highly-toxic substance, which can cause death, caused minor injuries to one mail clerk, but the letters never made it to her intended targets.

The 36 year old, also known as Shannon Guess Richardson, appeared in a federal court in Texarkana, Texas on Wednesday (16Jul14), when she used the opportunity to apologise to her victims, stating, "I never intended to hurt anyone."

Richardson was ordered to spend the next 18 years in a federal prison. Once completed, she must also spend five years on supervised release and pay $367,000 (£215,882) in restitution.

She had initially blamed her estranged husband Nathaniel Richardson for sending the letters. He filed for divorce last year (Jun13).