The U.S. dropped charges against a Mississippi man accused of sending ricin-laced letters to President Barack Obama and a U.S. senator, and federal agents searched the house of an acquaintance with whom the man said he had a bitter dispute, in a major turn of events in the high-profile case.

A federal judge signed a court order Tuesday dismissing the case against Paul Kevin Curtis, 45 years old, 'without prejudice,'' meaning that prosecutors could, in theory, reinstate the charges later if they found more evidence.

The court documents offer little explanation for why the charges were dropped, saying only that 'the ongoing investigation has revealed new information.''

After Mr. Curtis's release from federalcustody in Oxford, Miss., on Tuesday, agents from the Federal Bureau of Investigation searched the Tupelo, Miss., home of J. Everett Dutschke.

Mr. Dutschke was named this week by Mr. Curtis's lawyer as the person embroiled in a dispute with Mr. Curtis.

A law-enforcement official said the FBI is now probing the apparent feud between the two men to see if that explains the letters sent to Washington.

Mr. Dutschke's attorney, Lori Nail Basham, said her client was 'cooperating fully' with agents and had allowed them to search his home. She said her client hasn't done anything wrong and hasn't been charged with any wrongdoing.