Thomas Tholen, 54, was indicted on a charge of misprision of felony. U.S. Attorney Brett Tolman said Tholen knew ricin had been illegally produced but did not report it to authorities and lied to cover up his concealment.
"The consequences of this action could have been disastrous," Tolman said.
Tholen's cousin, Roger Bergendorff, remains in a Las Vegas hospital and is a target of the investigation, said Tim Fuhrman, special agent in charge of the FBI's Salt Lake City field office. Bergendorff hasn't been charged.
Fuhrman said investigators have turned up no evidence suggesting the ricin was part of a broader or indiscriminate terrorist plot. Rather, they believe the ricin was made in the Salt Lake City area and was to have been used for criminal purposes.
At a news conference, Tolman and Fuhrman repeatedly brought up a possible "lone wolf scenario" in which the ricin would be used selectively to harm someone.
Greg Skordas, an attorney for Tholen, said his client cooperated with authorities during an interview and a search of his house, and that Tholen can't explain the ricin's existence because "there isn't anything to explain. It wasn't his."
Skordas said Tholen answered FBI investigators' questions, but that agents "feel he knows more than he's letting on."
Bergendorff, 57, an unemployed graphic artist, summoned an ambulance from his Las Vegas motel room Feb. 14, complaining of respiratory distress. He spent almost four weeks in a coma, regaining consciousness March 12, and has been treated for kidney failure. It hasn't been determined if Bergendorff was sickened by the ricin.
Tholen was collecting Roger Bergendorff's belongings from the motel room on Feb. 28 when he gave a motel manager a plastic bag containing several vials of what turned out to be ricin powder.
The manufacture or possession of ricin, a biological agent, is prohibited by federal law.
Authorities who searched Tholen's house in the Salt Lake city suburb of Riverton and a storage shed haven't determined where the ricin was made, but are certain the extract of castor beans was made in this area and that Tholen knew about it, Fuhrman said.
"This is an ongoing investigation," FBI spokesman David Staretz in Las Vegas said Wednesday, declining comment.
Spring Valley Hospital spokeswoman Naomi Jones said Bergendorff remained in fair condition and was not under protective custody. "He's being treated like any other patient at the hospital," she said.
Bergendorff's brother, Erich Bergendorff, has said it's not clear if Roger Bergendorff made the ricin or watched someone else make the powder.
The charge against Tholen carries a maximum penalty of three years in prison. He wasn't arrested but will be sent a summons to appear in U.S. District Court in Salt Lake City.
A spokesman for Las Vegas police, Sgt. John Loretto, referred questions to the FBI.
