According to Richard Mederos, detective sergeant of the Harvard University Police Department (HUPD), the letters were sent in white, business-size envelopes postmarked from Las Vegas. They did not have a return address.

Only one of the letters was opened and no one was injured, Mederos said.

Mederos said that all letters have been passed on to the FBI, which will oversee a national investigation of this case.

Mederos said he believes this is the first time the University has been targeted by Justice Department, a group that has long employed violent measures.

The group's Web site explains their violent means by saying, "Animals had suffered long enough--the time has come for abusers to have but a taste of the fear and anguish their victims suffer on a daily basis."

In June 1994, Justice Department sent six letter bombs to companies involved in live exports of animals from North America to Europe.

In 1996, 65 envelopes with rat poison-covered razor blades were sent to hunting guides in Canada. Justice Department followed this threat by sending 87 envelopes containing razor blades allegedly tainted with AIDS-infected blood to Canadian fur retailers.