Investigators have claimed Shannon Rogers Richardson, also known as Shannon Rogers Guess, was responsible for mailing the letters.
Officials found evidence at the actress' house after she called to report she had found suspicious containers belonging to her husband in the couple's New Boston home. Law enforcement officials told CNN's Susan Candiotti that they believe Richardson sent the letters herself and that she was angry at her husband.
Last week, CNN reported that officials had "serious credibility issues" when they began interviewing Richardson.
Richardson has had minor roles in TV series "The Walking Dead" and "The Vampire Diaries."