OXFORD, Miss.  — Investigators haven’t found any ricin in the house of a Mississippi man accused of mailing poisoned letters to President Barack Obama, a U.S. senator and a local judge, according to testimony Monday from an FBI agent.

Agent Brandon Grant said that a search of Paul Kevin Curtis’ house in Corinth, Miss., on Friday did not turn up ricin or ingredients for the poison. A search of Curtis’ computers has found no evidence so far that he researched making ricin.