AUSTIN, Texas (NYTIMES) - Police responded to a reported explosion and injury at a strip mall south of downtown Tuesday evening (March 20), apparently the seventh bomb and sixth explosion in less than four weeks as a serial bomber continues to terrorise Texas' capital.

The bomber has not officially communicated with investigators. Yet, in some subtle ways, the bomber is doing just that with each explosive-rigged package that is found.

Law enforcement officials investigating one of the most brazen and deadly serial explosion cases in America in decades are struggling to read his bombs for any clues they can find. So far, five homemade explosive devices planted in packages and near sidewalks have detonated in Austin and near San Antonio this month, killing two people and wounding five.

Earlier on Tuesday, a sixth bomb, this one unexploded, forced the shutdown of a FedEx facility near Austin's airport. Officials have launched a sweeping manhunt, both forensic and physical, for the bomber, whose identity and motive remain unknown.

"It's such a random sending of these bombs," said Nelson Wolff, the top elected official in Bexar County, which includes San Antonio. "You've got somebody out there, or possibly more than one person, that's obviously got a system going, and that doesn't mean it couldn't be changed from one town to the other."

The FBI confirmed on Tuesday night that the two latest packages located at FedEx facilities near San Antonio and Austin airport were connected to the earlier explosions.

The explosions do not destroy evidence of the bombs' origins so much as blast it into many bits and pieces; DNA and other more technical fingerprints can remain. And one new potential block of evidence emerged on Tuesday from the Austin bomber's use of FedEx.

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.