The device that killed Patrick Hsu two weeks ago was a mail bomb delivered to the teenager's San Jose home, the U.S. Postal Service confirmed yesterday.

The disclosure came as postal investigators announced that an award of up to $100,000 is being offered for information leading to an arrest and conviction of any person involved in the Feb. 10 attack.

Hsu, an 18-year-old freshman at the University of California at Santa Barbara, was visiting his family for the weekend when he was killed by an explosive device contained in a package delivered to the Tulip Blossom Court home.

Hsu's family have said that they believe a package containing a robotic toy dog delivered in mid-January was the device that killed the young man. Chen Hsu, the victim's father, told reporters the dog might have exploded when his son placed a battery in it.

Yesterday, both the postal service and San Jose police continued to keep a tight lid on the investigation, declining to comment on the case except to confirm the mail bomb.

"There's very little detail I can tell you, but we can say we have determined that (the bomb) was delivered to the Hsu home through the regular U. S. mail," said postal inspector Michael Baum.

The $100,000 award is the maximum offered by the postal service.

"It's the standard amount for the crime of murder," Baum said. "How much of it can be claimed would depend on the significance of the service a person would give us, or any risks or hazards involved or expenses incurred."

©2001 San Francisco Chronicle