Two Senate buildings reopen after anthrax testing

Investigators say the Leahy and Dashcle letters are similar.

WASHINGTON (CNN) -- Two Senate office buildings that had been closed over the weekend for anthrax testing reopened Monday morning.

The Russell and Dirksen buildings had been closed for environmental sampling after a letter similar to an anthrax-laced missive sent to Senate Majority Leader Tom Daschle, D-South Dakota, was discovered Friday in a barrel of quarantined mail. Addressed to Sen. Patrick Leahy, D-Vermont, it was sent to Fort Detrick, Maryland, for testing after initial tests came back "presumptive positive" for anthrax.

Investigators said they hope to find new clues to the origin of the letters.

Evidence in the letters addressed to Daschle, NBC News anchor Tom Brokaw and The New York Post was destroyed when the letters were opened and anthrax spores escaped into the air, investigators said.

The Leahy letter was found Friday by hazardous materials experts wearing environmental protection suits who were sorting through 280 barrels of mail addressed to Capitol Hill. The barrels have been quarantined at a facility in Virginia since the discovery of an anthrax-laden letter sent to Daschle, which one of his staffers opened on October 15 in the Hart Senate Office Building.

The Hart building, where the Daschle letter was sent last month, remains closed.

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Investigators have gone through all the barrels of congressional mail at the facility in Virginia, but cannot be certain no more like those sent to Daschle and Leahy exist, an FBI official said. The reason: Some mail bound for lawmakers is part of the batch of mail sent from the Brentwood postal facility in Washington to be sanitized in Ohio.

The U.S. government is offering a $1.25 million reward for information leading to the arrest of the mailer of anthrax-laced letters, the FBI said.