Curtis has been charged by the government with threatening the life of the president.
Senator Wicker said Thursday he once hired the 45-year-old as an Elvis impersonator for an engagement party.
Curtis' attorney said her client is surprised by the charges against him. A preliminary hearing is set for Friday.
OXFORD, MS (WREX)—Mississippi man was arrested Wednesday, accused of sending letters to President Barack Obama and a senator that tested positive for the poisonous ricin and set the nation's capital on edge a day after the Boston Marathon bombings.
The FBI has identified him as 45-year-old Paul Kevin Curtis.
FBI Special Agent in Charge Daniel McMullen said Curtis was arrested Wednesday afternoon at his apartment in Corinth, near the Tennessee state line about 100 miles east of Memphis.
Both letters said: "To see a wrong and not expose it, is to become a silent partner to its continuance." Both were signed, "I am KC and I approve this message."
The letters were intercepted before reaching the White House or Senate. The FBI said Wednesday that more testing was underway. Preliminary field tests can often show false positives for ricin.