US authorities have dropped the charges against a Mississippi man accused of sending letters poisoned with ricin to President Barack Obama and a senator.
Paul Curtis was freed on Tuesday after prosecutors revealed the investigation had uncovered "new information".
The letters addressed to the president and a Mississippi senator tested positive for the presence of the lethal toxin this month.
Meanwhile, investigators in the case are searching the home of another man.
Mr Curtis was arrested last week at his home in the town of Corinth, Mississippi and charged with sending letters to Mr Obama, Republican Mississippi Senator Roger Wicker and a judge from Lee County.
But on Monday authorities searched Mr Curtis' home and found neither ricin nor ingredients for the poison, an FBI agent testified in court. A search of his computer yielded no evidence he had researched how to make the toxin, the agent said.