TEXARKANA, Texas — An actress pleaded guilty in federal court Tuesday to making the toxic agent ricin that was sent in letters to President Obama and Mayor Bloomberg.

As part of a deal reached with federal prosecutors that has yet to be approved by a judge, actress Shannon Guess Richardson, 36, would spend 18 years in prison and then five years on supervised release, according to court documents.

Richardson, whose career included minor television roles in shows such as “The Walking Dead,”
tried to blame her husband for the letters, sent in May, which tested positive for the presence of ricin, according to prosecutors.