WASHINGTON, D.C.: The FBI investigation of eight letter bombs disguised as musical Christmas cards has turned toward the federal penitentiary in Leavenworth, Kansas that is home to Mohammad Salameh, one of four people convicted in the 1993 World Trade Center bombing. "We are treating it as a terrorism matter," FBI spokeswoman Susan Lloyd said. The bombs discovered Thursday, carrying a postmark of Alexandria, Egypt, were mailed in plain, white, 5 1/2 by 6 1/2 envelopes with computer-generated addresses and no return addresses. Four went to the Washington office of an Arabic newspaper, Al Hayat, at the National Press Building, and one was found at a post office handling the newspaper's mail. Two similar cards were sent to the prison itself, addressed to an unnamed "parole officer." None of the bombs exploded, and no one was injured. Said one federal law enforcement official, who asked not to be identified: "We will be studying the ethnic makeup of that prison's population in the course of our investigation. We have drawn no conclusions, but this is one obvious area to look at." For now, the FBI is warning the rest of us. "We're concerned that there could be additional such letters still in the mail," agent Raymond Mislock said. "We would very much like anyone who identifies a similar piece of mail not to touch it or disturb it any way." The FBI said anyone who receives similar mail should notify their local police department or postal inspectors, or call the FBI's terrorism task force at 202-252-7001.