NEW YORK -- A Postal Service parcel that exploded and killed an advertising executive in his suburban New Jersey home is believed to be the handiwork of a mysterious serial bomber -- dubbed Unabomb by the FBI -- who has conducted a 16-year reign of terror.


In the wake of the death of Thomas Mosser, investigators are stepping up a manhunt for a suspect they think is behind at least 13 bombings.


Mosser, general manager and executive vice president at Young & Rubicam Inc. in New York, died Saturday morning while opening a rigged parcel. He was the second man killed in an explosion traced to the suspect in the Unabom bombings since 1978.


Investigators say the suspect has targeted computer company owners and employees, professors and airline executives in his bloody spree, which has injured a total of 23 people. One bomb exploded on a plane in 1979, injuring 12. The name Unabomb applied to the bomber is derived from the combination of university and airliner -- the sites of the first three explosions.


The U.S. Federal Bureau of Investigation describes the suspect as a white male in his 30s or 40s, with at least a high school degree and possibly a college education.


"He is very good at what he is doing, unfortunately," said Barry Mawn, the special agent-in-charge of the FBI's Newark, New Jersey office.


"These are sophisticated packages. He puts them together well," Mawn said. "By its very nature, a bomb blows up much of the evidence."