Courthouse Bombing Has MO of Serial Bomber

May 4, 2008 — -- An explosion early this morning at the federal courthouse in San Diego may be the work of a serial bomber who in April set off bombs at a Federal Express facility in the city, law enforcement officials said.

According to authorities, it appears the explosive device was inside a backpack. The bomber placed the device at the doors to the Edward J. Schwartz United States Courthouse, lit the fuse and fled, officials said.

The device was described by authorities as made of three galvanized pipe bombs, measuring 1-by-10 inches, and two 3-by-8 inch explosives.

The method of attack was similar to the April 25, 2008, explosion at a FedEx facility in San Diego. That bombing occurred about 2 a.m. This one was set off at 1:40 a.m., according to an FBI press statement.

The attacks do not appear linked to any of the early morning blasts that have plagued New York City in recent months. In those instances, the explosives were made from military casings -- ammo boxes and grenades -- filled with black powder. They also were triggered by lighting a fuse. The New York bomber was seen leaving on a bike.

According to the FBI, the explosion in San Diego shattered a glass door, damaged the lobby and punched a hole in a building window across the street. No one was reported injured.

ABC News' Jason Ryan contributed to this report.