OGDEN -- The resolve of Americans is greater than any series of attacks and threats on the nation or its leaders, says Rep. Chris Stewart, R-Utah.
"In the past few days, we have all dealt with unspeakable things -- the bombings in Boston, a contaminated letter to the Senate and now a contaminated letter to President (Barack) Obama," said Allison Barker, speaking for Stewart's Washington D.C. office.
Stewart's comments are in response to news of letters addressed to President Obama and Sen. Roger Wicker, R-Mississippi, testing positive for poisonous ricin in preliminary checks.
The letters sent to Obama and Wicker had authorities chasing a stream of false alarms about seemingly suspicious packages and mail sent to senators in Washington and beyond.
A Mississippi man was arrested Wednesday, accused of sending the letters to the president and senator that tested positive for the poisonous ricin.
FBI Special Agent in Charge Daniel McMullen said Paul Kevin Curtis, 45, was arrested at 5:15 p.m. at his apartment in Corinth, near the Tennessee state line about 100 miles east of Memphis. It wasn't immediately known where he was being held.
Authorities still waited for definitive tests on the letters to Obama and Wicker, which had raised concern Wednesday at a time when many people were jittery after the Boston bombings.
An FBI intelligence bulletin obtained by The Associated Press said those two letters were postmarked Memphis, Tenn. Both letters said: "To see a wrong and not expose it, is to become a silent partner to its continuance." Both were signed, "I am KC and I approve this message."
The letters were intercepted before reaching the White House or Senate. The FBI said Wednesday more testing was under way. Preliminary field tests can often show false positives for ricin.
"The American people have an unwavering resolve. Now more than ever, communities across this great nation need to come together in love and support, as we have always done in the face of danger or tragedy," Stewart told the Standard-Examiner by email Wednesday.
Stewart represents Utah's 2nd Congressional District.
"For us it is business as usual until something changes," said Melissa Subbotin, spokeswoman for Rep. Rob Bishop, R-Utah.
Subbotin said the Senate office is a distance away from their House office location.
But anytime a threat is made on a president or member of Congress, Subbotin said, it is a concern.
Republican Sen. Mike Lee's Washington D.C. office expressed its confidence in those watching over the nation's Capitol.
"I am grateful for the swift and efficient work of the FBI and our law enforcement agencies, as well as the Capitol Hill police who clearly have the right policies and procedures in place to keep members and staff safe," Lee said through press secretary Emily Bennion.
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.
Messages left with the office of Sen. Orrin Hatch, R-Utah, were not returned.
As authorities scurried to investigate three questionable packages discovered in Senate office buildings, reports of suspicious items also came in from at least three senators' offices in their home states.
Sen. Carl Levin said a staff member at his Saginaw, Mich., office would spend the night in a hospital as a precaution after discovering a suspicious letter. The staff member had no symptoms, Levin said in a statement. He expected to learn preliminary results of tests on the letter by today.
Sen. Jeff Flake, R-Ariz., said suspicious letters at his Phoenix office had been cleared, with nothing dangerous found. A package at Sen. John Cornyn's Dallas-area office also was declared harmless, a fire department spokesman said.
All three packages in the Capitol complex turned out to be safe, Capitol police spokeswoman Makema Turner said late Wednesday. But a man was still being questioned after being stopped in connection with the packages, she said.
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.
At a House hearing, Postmaster General Patrick Donahoe noted that no postal workers have reported any illness connected to the incident. Ricin, derived from the castor plant, is at its deadliest when inhaled.
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.
-- Associated Press writers Connie Cass, David Espo, Donna Cassata, Henry Jackson, Pauline Jelinek, Richard Lardner, Alan Fram, Ken Thomas, Jim Abrams, Andy Taylor, Seth Borenstein and Eric Tucker contributed to this report.