As testing for the spread of the toxin ricin continues to yield negative results, Senate leadership announced that the Hart and Dirksen office buildings may open as early as today.

“The schedule for opening the Hart and Dirksen Office Buildings is being reevaluated with the possibility of the Hart building opening today and the Dirksen building opening earlier than Monday, Feb 9th,” states an e-mail sent to Senate employees late Thursday morning. The Russell Building opened at noon today.

All three Senate office buildings were closed early Tuesday morning after tests identified ricin in Senate Majority Leader Bill Frist’s (R-Tenn.) personal office in the Dirksen Building.

In an announcement on the chamber floor Wednesday afternoon, Frist said Hart would not reopen until 9 a.m. Friday, followed by Dirksen on Monday at 7 a.m., with the exception of his fourth-floor personal office, which is being treated as a crime scene by Capitol Police.

The police, assisted by the Marines and Coast Guard, have been collecting unopened mail from the Capitol and House and Senate office buildings since Tuesday evening. Capitol Police Chief Terrance Gainer noted Thursday that the Capitol and the Rayburn House Office Building had been swept for mail and tested for evidence of ricin.

At a Thursday press conference Gainer acknowledged those efforts are “a little bit ahead of schedule,” but he would not confirm if the Hart or Dirksen buildings would be open earlier than expected.

“Substantial progress continues to be made to reclaim the buildings,” said Gainer, who was flanked by representatives of the Attending Physician’s Office, Coast Guard, Marine Chemical-Biological Incident Response Force, FBI and Environmental Protection Agency. Gainer later added: “The schedule we’ve laid out is a good one, we’re trying to exceed that.”

According to separate e-mails sent to House and Senate staff, environmental sampling began at 8 a.m. Thursday in the Hart Building and mail collection for testing is scheduled to begin in the Longworth House Office Building at 7 p.m.

“All Senate Office Building environmental samplings continue to be negative,” the Senate e-mail states. There have also been no positive test results reported in the House office buildings.

Senate officials also continue to stress that no one exposed to the toxin — which is derived from castor beans — has shown symptoms of illness. There is no antidote for exposure to ricin poisoning.

“Nationwide, there have been no Public Health reports of Ricin poisoning symptoms,” the Senate e-mail states. A representative of the Attending Physician’s Office said Thursday that officials now do not expect anyone to develop symptoms or become ill.

In the meantime, Capitol Police and FBI agents are continuing to search for the letter or package that contained the toxin.

“We have not found a hot letter at this time,” said Mike Mason, assistant director of the FBI’s Washington field office. Although agents have screened mail collected from Frist’s office, Mason said, forensic tests of the materials have not been completed, and could still identify an envelope contaminated with ricin.

Similarly, officials stated Thursday they have not determined how the ricin-laced package arrived in Frist’s office. Following a Wednesday press conference, however, Gainer said officials had ruled out local UPS and FedEx facilities.

Mason said that a “relatively small” amount of ricin was found in the fourth-floor office; however, he declined to provide specific details on the amount.