Specialists from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives who are working the case have honed their skills, and their eyes, for years. The A.T.F. has long run a five-day “post-blast investigator” course for law enforcement around the country. Typically, once the classroom portion of the course has ended, the agency will blow up a car on a demolition range using a real car bomb, and the students will comb the range afterward for parts and pieces of the device that exploded.

At the scene of the first package explosion in Austin, a red brick house on Haverford Drive in northeast Austin where the first victim, Anthony Stephan House, 39, was killed, a large chunk of the white-painted wall next to the plywood-covered front door has been removed, probably by investigators who want to recover minuscule bomb fragments from it.

“The Unabomber put ‘FC,’ which stood for Freedom Club, on his bombs, so the investigators will be looking for any signatures that could give them some investigatory leads,” said Clinton R. Van Zandt, a former profiler with the F.B.I. who worked on the case. The bomber, Theodore Kaczynski, was a mathematics professor turned recluse whose crudely fashioned bombs killed three people and injured 24 others over a 17-year period beginning in 1978.

One new potential block of evidence emerged on Tuesday from the Austin bomber’s use of FedEx.

The package that exploded shortly after midnight Tuesday at the FedEx center in Schertz, outside San Antonio, was shipped from the Austin area and was bound for Austin as well. Another suspicious package discovered on Tuesday also was shipped via FedEx, and it, too, contained explosive material, a law enforcement official said.

Both packages were mailed from a FedEx store in Sunset Valley, a small city within Austin, and a statement from FedEx suggested that they were sent by the same person.

The second package was turned over intact to law enforcement, marking the first time investigators will get their hands on one of the serial bomber’s unexploded devices. They may also be able to get video images of the person who shipped it.