OXFORD (AP) — Investigators haven’t found any ricin in the house of 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’ vehicle and 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.

“There was no apparent ricin, castor beans or any material there that could be used for the manufacturing, like a blender or something,” Grant testified. He speculated that Curtis could have thrown away the processor. Grant said computer technicians are now doing a “deep dive” on the suspect’s computers after initially finding no “dirty words” indicating Curtis had searched for information on ricin.

Through his lawyer, Curtis has denied involvement in letters sent to Obama, Mississippi Republican Sen. Roger Wicker, and a Lee County, Miss., judge. The letters, bearing a Memphis, Tenn., postmark, were detected beginning April 15.

Curtis’ lawyer said in court that someone may have framed Curtis, suggesting that a former co-worker with whom Curtis had an extended exchange of angry emails may have set him up.

Still, Grant testified that authorities believe that they have the right suspect.

“Given the right mindset and the Internet and the acquisition of material, other people could be involved. However, given information right now, we believe we have the right individual,” he said.

Grant said lab analysis shows the poison is a crude form that could have been created by grinding castor beans in a food processor or coffee grinder.

“That would be a low-tech way of doing it. You’re just blending up the beans to get the ricin that’s on the inside on the outside,” Grant testified.

The detention and preliminary hearing began Friday in U.S. District Court in Oxford, Miss., but was continued until Monday when it ran into the evening. After several hours of testimony, the judge adjourned the hearing until Tuesday morning.

Federal investigators believe the letters were mailed by Curtis, an Elvis impersonator who family members say suffers from bipolar disorder. He wore an orange jumpsuit from the Lafayette County Detention Center in court Monday, and was quiet and attentive, sometimes whispering to Christi McCoy, his lawyer

McCoy continued Monday to emphasize that the federal government has produced little physical evidence linking her client to the crime. She said she would seek to have U.S. Magistrate Judge J. Allan Alexander declare there was no probable cause that Curtis committed the crime and have him released.

Grant testified Monday that processing codes printed on the letter indicated they had been mailed from Tupelo, and that investigators were still trying to figure out from the codes exactly where they had been mailed.

Grant testified Friday that authorities tried to track down the sender of the letters by using a list of Wicker’s constituents with the initials KC, the same initials in the letters. Grant said the list was whittled from thousands to about 100 when investigators isolated the ones who lived in an area that would have a Memphis, Tenn., postmark, which includes many places in north Mississippi. He said Wicker’s staff recognized Curtis’ name as someone who had written the senator before.

The letters also contained lines that were on Curtis’ Facebook page, including the phrase, “I am KC and I approve this message,” Grant said.

Grant also testified that there were indentations on the letters from where someone had written on another envelope that had been on top of them in a stack.

The indentations were analyzed under a light source and turned out to be for Curtis’ former addresses in Booneville and Tupelo, though the street name in one of the addresses was spelled wrong, Grant said.

All the envelopes and stamps were self-adhesive, Grant said Monday, meaning they won’t yield DNA evidence. He said thus far the envelopes and letters haven’t yielded any fingerprints.

McCoy said the evidence linking the 45-year-old to the crime has hinged on his writings posted online, which were accessible to anyone.

Much of Monday’s testimony focused on Curtis’ prior run-ins with police and evidence about his mental health.

“The fact that this man may be suffering from a form of mental illness, how does this make it make it more likely than not that Mr. Curtis committed to these crimes?” McCoy asked.

Grant said that it didn’t, but said past evidence about mental state, “helps establish a potential behavior background for Mr. Curtis, perhaps not realizing what he’s doing.”