Paul Kevin Curtis, 45, is "believed to be responsible for the mailings of the three letters sent through the U.S. Postal Inspection Service which contained a granular substance that preliminarily tested positive for ricin," the FBI said.
Along with Obama, the other intended recipients were Mississippi Republican Senator Roger Wicker and a justice official in the state, according to an FBI statement. None of the envelopes reached their intended target.
Curtis is scheduled to make an initial federal court appearance on Thursday. He could be sentenced to a maximum of 15 years in prison if found guilty of threatening the president and others, the Associated Press reported.
Two rounds of analysis indicated the Obama and Wicker letters contained the lethal toxin, the Washington Post reported. Further testing is planned, according to one law enforcement source.
A number of other suspicious packages found on Capitol Hill and in legislators' home-state offices proved harmless. However, the incidents heightened tensions already spiked by Monday's bombing at the Boston Marathon.
Curtis is said to have a history of writing to lawmakers. The letters to Obama and Wicker both stated, "To see a wrong and not expose it, is to become a silent partner in its continuance," Reuters reported. The writer added, "I am KC and I approve this message."
The suspect also has indicated he was investigating the illicit sale of body parts and that "various parties within the government" were working against him, AP reported.
Someone named Kevin Curtis used a similar sign-off in a 2007 web statement charging misconduct in Elvis impersonation events held in several states.