Everett Dutschke, 41, was arrested early Saturday morning at his Tupelo home. The letters, which allegedly contained the poison ricin, were sent last week to the president, Sen. Roger Wicker of Mississippi and earlier to an 80-year-old Mississippi judge, Sadie Holland.
FBI spokeswoman Deborah Madden said that Dutschke was arrested without incident. His attorney had no comment.
Charges in the case were initially filed against an Elvis impersonator but then dropped. Attention then turned to Dutschke, who has ties to the former suspect and the judge and senator.
The Associated Press contributed to this report.