Gainer said the man was "not particularly harmful, although terribly disruptive."
All the activity came as tensions were high in Washington and across the country following Monday's bombings at the Boston Marathon that killed three people and injured more than 170. The FBI said there was no indication of a connection between the letters and the bombing. The letters to Obama and Wicker were postmarked April 8, before the marathon.
Obama's press secretary, Jay Carney, said mail sent to the White House is screened at a remote site for the safety of the recipients and the general public. He declined to comment on the significance of the preliminary ricin result, referring questions to the FBI.
Capitol Police swiftly ramped up security, and lawmakers and staff were cautioned away from some parts of the Hill complex. After hours of jangled nerves, officials signaled it was safe to move throughout the area and people settled back to normal, if watchful, activity.
At a House hearing, Postmaster General Patrick Donahoe noted there had been ricin alerts since the notorious 2001 anthrax mailings and procedures are in place to protect postal employees and help track down culprits.
"Over the course of years we've had some situations where there have been ricin scares," Donahoe said. "Until this date, there's never been any actually proved that have gone through the system."
Wicker in a written statement thanked the FBI and U.S. Capitol Police for "their professionalism and decisive action in keeping our family and staff safe from harm."
Even during the flurry of concern, normal business continued across most of the Capitol and its office buildings, with tour groups passing through and visitors streaming in and out of Wicker's office.
Amy Keough of Stow, Mass., and her family were searching for an open entrance to the Russell Senate Office building and walked by a U.S. Capitol Police hazardous materials vehicle. The Keoughs had been visiting Washington for several days, but Monday's marathon bombing was on their minds.
"We don't know really what it is that's going on," Keough said. "We're from Massachusetts, so right now anything is possible, with all the events in Boston."