With tests showing no new traces of poisonous ricin in the Capitol complex, senators and their staff returned Feb. 5 to the first of three closed office buildings, with hopes that the others would reopen soon, The Associated Press reported.

The Russell Senate Office Building, the oldest and closest to the U.S. Capitol of the three Senate office buildings, reopened around noon. Hill staffers waited in lines to get back to work.

Senators also were anxious, after two days crowded into small Capitol offices and space borrowed from their House colleagues. Many of them have been working off Blackberry wireless communicators, home e-mail and cell phones since they didn't have access to their office files and computers, The AP reported.

“I'm anxious to get back to work, because it's been so disorienting being out of my office,” said Sen. Olympia Snowe, R-ME, who has a first floor office in the reopened building but has been working out of a Capitol office.

Meanwhile, officials said they still didn't know how ricin arrived in the mailroom of Senate Majority Leader Bill Frist.

A thorough search of Frist's mailroom turned up no additional traces of ricin and no threatening letters or messages, two days after a powdery form of the deadly toxin was found in Frist's suite in the Dirksen Senate Office Building.

A letter with ricin found in October at a postal facility serving South Carolina’s Greenville-Spartanburg International Airport was signed “Fallen Angel.” Another ricin letter signed the same way was found in November at a facility that processes mail for the White House. Both letters complained about new hours-of-service regulations for truckers, which became effective Jan. 4.

In the meantime, officials were investigating whether the ricin incident involving Frist’s mailroom was related to these earlier incidents, according to press accounts.