Investigators have not found ricin or ingredients for it in the house or vehicle of a Corinth man accused of mailing poisoned letters to President Obama, a senator and a local judge, an F.B.I. agent testified Monday.  http://www.nytimes.com/aponline/2013/04/23/us/ap-us-suspicious-letters.html?ref=us  A search of a computer belonging to the man, Paul K. Curtis, found no evidence that he researched making ricin, Agent Brandon Grant said. Through his lawyer, Mr. Curtis has denied involvement, and his lawyer said he may have been framed.  “The searches are concluded, not one single shred of evidence was found to indicate Kevin could have done this,” The evidence linking the 45-year-old to the crime has hinged on his writings posted online, which were accessible to anyone.