On its Web site, a radical group calling itself the "Justice Department" claims it mailed more than 80 razor-edged envelopes to animal researchers from Harvard to California.
"You have until autumn of 2000 to release all your primates," it warned. "If you do not heed our warning, your violence will be turned back upon you."
Dr. Peter Gerone of Tulane University in New Orleans received a letter and gave it to authorities.
"The razor blade was inserted into the flap on the inside, and it was glued to the 'v' of the flap," Gerone explained.
More than three of the letters went to the one of the country's largest primate research centers, at the University of California, Davis. The research center has produced breakthroughs in AIDS, Alzheimer's and micro-surgery. University security was tightened up, but center director Jeffrey Roberts says the targeted scientists are afraid to appear on camera.
"What we are talking about are compassionate people," Roberts said. "These people are involved in this research because they care about humans. They care about human health."
"The animal rights movement in the United States is becoming a very serious threat to human life," said Ron Arnold, author of Ecoterror.
The FBI is investigating now. It's believed more razor letters are in the mail. And with animal rights zealotry heating up, it's feared more researchers are in harm's way.