Investigators found no traces of ricin in the house of the Mississippi man accused of mailing the toxic letters to President Obama, a senator and local judge, the Associated Press reports.
Agents believe Paul Kevin Curtis sent the letters but they have been unable to find evidence, including on his computer.
Curtis’ lawyer suggested the suspect was set up.
FBI Agent Brandon Grant disagrees.
“Given the right mind-set and the Internet and the acquisition of material, other people could be involved,” Grant said. “However, given information right now, we believe we have the right individual.”