(AP) - Defense lawyers for a man accused of mailing poisoned letters to President Barack Obama, a U.S. senator and a local judge say investigators' failure to find any ricin means the government should release their client. That lack of physical evidence could loom large as a detention and preliminary hearing continues Tuesday morning. U.S. Magistrate Judge J. Allan Alexander ended the hearing after lunch Monday, citing a personal schedule conflict. FBI agent Brandon Grant told the court Tuesday that searches of Paul Kevin Curtis' vehicle and house in Corinth, Miss, have found no ricin. A search of Curtis' computers has found no evidence he researched making the poison. Through his lawyer, Curtis has denied involvement in letters sent to Obama, Mississippi Republican Sen. Roger Wicker, and a Lee County, Miss., judge.