According to Bloomberg, Grant testified that the letters, intercepted at off-site screening facilities last week, included a "very crude form of ricin," as if someone had "put castor beans into a food processor or blender and ground them up.” 

According to the Centers for Disease Control, the poison, extracted from castor beans, is highly toxic if even a small dosage is inhaled or ingested.

Curtis has denied involvement in the letters, which were postmarked April 8 and bear a Memphis, Tenn. postmark. According to Bloomberg, the letters were signed "I am KC and I approve this message." The 45-year-old faces a maximum of 15 years in prison if convicted of using the mail to convey threats to public officials, including President Obama.

Wicker, speaking to reporters at the Capitol last week, said he knew Curtis from "social events" during his time serving in the House of Representatives.

Well, he’s an entertainer. He’s an Elvis impersonator," Wicker said. "He entertained at a party that my wife and I went to. ... My impression is that about that time he had some mental issues, and was perhaps not as stable. A number of couples threw the party ... and we kicked in [money to pay him] I’m sure."