A man from Corinth, Mississippi, Paul Kevin Curtis, was arrested on Wednesday at 5:15 pm. He is believed to be the man responsible for mailing three letters through the U.S. Postal Service believed to contain ricin.

The three letters were mailed to the White House, U.S. Senator Roger Wicker, and a Mississippi Justice official.

Curtis was arrested at his home in Corinth following the investigation into the letters by the FBI Joint Terrorism Task Forces in Memphis, Tennessee, and Jackson, Mississippi, the U.S. Capitol Police, the U.S. Postal Inspection Service and the United States Secret Service. Those investigators were also aided various state and local agencies in Mississippi as well as the Department of Homeland Security.

In a statement, the Justice Department said, “the individual believed to be responsible for the mailings of the three letters sent through the U.S. Postal Service which contained a granular substance that preliminarily tested positive for ricin.”

More tests on the letters have been ordered. The preliminary tests showed the presence of Ricin, but the tests did not determine the level of the potency of that substance. The results of the full tests can be expected in 24 to 48 hours.

In the letters mailed on April 8th, a portion of the message contained said, “To see a wrong and not expose it is to become a silent partner to its continuance. I am KC and I approve this message.”