A US actress has pleaded guilty to making the highly toxic agent ricin that was sent in letters to President Barack Obama and New York Mayor Michael Bloomberg in May this year.
Shannon Guess Richardson, from Texas, whose career included minor roles in TV shows such as The Walking Dead and The Vampire Diaries pleaded guilty to charges of manufacturing and possessing the biological agent ricin, which was found in the letters.
As part of a deal reached with federal prosecutors that has yet to be approved by a judge, the 36-year-old would spend 18 years in prison and then five years on supervised release, according to court documents.
A martial arts instructor from Mississippi has been arrested by US authorities investigating the ricin-laced letters sent to Barack Obama and other officials, police have told Reuters.
Everett Dutschke, 41, was taken into custody this morning from his Tupelo home, which was searched twice last week along with the premises of his former martial arts studio in the city.
US prosecutors dropped charges on Tuesday against another Mississippi man, Elvis impersonator Paul Kevin Curtis.
He was released from jail after a search of his home in nearby Corinth revealed no incriminating evidence.
An envelope sent to Republican Senator Roger Wicker of Mississippi tested positive for ricin, Senator Dick Durbin told reporters after a group of lawmakers were briefed by the FBI.
Ricin is a lethal poison found naturally in castor beans.
A spokeswoman for Mr Wicker referred inquiries to US Capitol Police, according to Reuters.
A spokesman for Capitol Police could not immediately be reached for comment.