A Mississippi martial arts tutor has been arrested over letters sent to President Obama and two other public officials containing the poison ricin.
Everett Dutschke, 41, was taken into custody by marshals without incident at 12:50am on Saturday at his home in Tupelo, said the town's police chief Tony Carleton.
For two days, agents from the FBI and the Capitol Police as well as members of the anti-terrorist response team of the Mississippi National guard had scoured his home and martial arts studio for evidence.
Earlier in the week, Dutschke had gone missing for a few days.
A law enforcement official told WTVA that the 41-year-old was being held at the Lafayette County Detention Centre, and that he would not appear in US District Court until Monday.
Earlier this year Dutschke was arrested and charged with molesting three girls, although he has not yet been put on trial over the allegations.
Elvis impersonator Paul Kevin Curtis, who has links to Mr Dutschke, was released after a search of his home provided no indication of his involvement in the plot.
Mr Curtis's lawyer, Hal Neilson, said that his client had provided police with a list of people who may have wished to do him harm and investigators "took it and ran with it."
Letters containing ricin were sent last week to President Obama, Senator Richard Wicker and Mississippi judge Sadie Holland.
The letters to Obama and Senator Wicker were intercepted at government mail sorting facilities before they could reach their addressees.
Ricin, made from castor beans, can be fatal to humans, and in its aerosol form can claim many lives.