FBI: Letter in Daschle's office a hoax

The letter was found in the Capitol office Daschle uses as majority leader.

WASHINGTON (CNN) -- An envelope containing a threatening note and a "powdery substance" found Thursday in the U.S. Capitol office of Senate Majority Leader Tom Daschle is likely a hoax, according to an FBI spokesman.

Two initial tests showed the powder was not hazardous, Lt. Dan Nichols of the Capitol Police said earlier Thursday.

Postmarked in London and dated in late November, the letter was triple bagged and taken to a U.S. Army lab at Fort Detrick, Maryland, for further analysis, government sources said.

"While we don't know exactly what it is, because it's still in the process of being investigated, we do know it's not hazardous," Nichols said.

Thursday's development came nearly three months after a letter containing a potent form of anthrax was opened October 17 at Daschle's office in the Hart Senate Office Building. Another letter, addressed to Vermont Sen. Patrick Leahy, was found before it was opened.

Since October, all mail coming into the Capitol complex is irradiated to render any anthrax harmless. A machine then cuts a corner off each letter and shakes it to see if there is a powder inside, congressional sources said.

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The letter found Thursday arrived via the U.S. mail and was subject to usual process before being sent to Daschle's office, Nichols said.

A member of Daschle's staff found the letter in the office used by the South Dakota Democrat in his role as Senate leader and called Capitol police at 11:40 a.m.

A hazardous materials team responded and tested the substance. The area was immediately sealed off and the historic building was closed until field tests showed the powder was harmless.

Nichols, who refused to discuss the letter's appearance, said the FBI has launched a criminal investigation.

Despite a recent fumigation completed Monday, the other offices of Daschle and 49 other senators in the Hart building remain closed, as they have been since October.

Even if the latest samples test negative for anthrax, the EPA said it has no timeline for when the building will reopen.