Scientists have determined that the anthrax powder sent through the mail last fall was fresh, made no more than two years before it was sent, senior government officials said. The new finding has concerned investigators, who say it indicates that whoever sent the anthrax could make more and strike again.

Establishing the age of the anthrax that killed five people has strengthened the theory that the person behind the mailings has a direct and current connection to a microbiology laboratory and may have used relatively new equipment. "We're still looking for someone who fits the criteria of training, knowledge, education, experience and skill," agovernment official said.

The new finding casts serious doubt on another theory that had complicated the so far fruitless investigation: that the culprit had stolen or somehow obtained an old laboratory sample of powdered anthrax, from a strain first identified in 1981.