SAN DIEGO -- The downtown federal courts complex was slated to reopen Tuesday morning following a one-day closure prompted by a powerful pipe-bomb blast that damaged the facility over the weekend.

A homemade device made of several connected tubes packed with some type of explosive material detonated outside the Edward J. Schwartz Federal Courthouse on Front Street about 1:40 a.m. Sunday, damaging a front door and lobby area and breaking a window on a nearby building.

The bomb was "specifically designed to fragment" like a military grenade, FBI Special Agent Keith Slotter told reporters Monday.

"So it was not just a device that would cause damage to the federal courthouse building, but it was designed to send shrapnel -- specifically a large quantity of nails -- out into the general area," he said.

"There's a very good chance someone could have been very seriously injured or even killed (due to) the way that that device was constructed," Slotter said.

The outcome could have been much different if the device had detonated on a busy workday instead of while the building was closed. Slotter noted that some of the shards and projectiles were found several blocks from the site of the explosion.

Investigators spent the last two days collecting crime-scene evidence and analyzing a surveillance video that captured the blast and images of several people in the area moments beforehand.

No one has taken responsibility for the crime, which did not immediately appear to be an act of terrorism or linked to any specific court case, according to the FBI.

Officials also said it was unclear if the attack was linked to a pipe-bombing that damaged a Federal Express building in the Webster area of San Diego late last month.