SAN DIEGO -- The FBI said Monday that it is looking into whether a pipe bomb attack at a downtown federal courthouse is linked to a blast at a FedEx office last month.

The courthouse explosion early Sunday spread nails and shrapnel as far as two blocks, potentially killing anyone caught in the way, said Keith Slotter, special agent in charge of the FBI's San Diego office.

Slotter said surveillance video shows "some individuals" in the area shortly before the explosion, but declined to elaborate.

Authorities have not identified any suspects and no one has claimed responsibility.

The FBI is determining whether the attack is related to a bomb that shattered the glass door of a FedEx building in San Diego around 2. a.m. on April 25. Authorities found a second bomb in the FedEx parking lot and detonated it.

"We are looking at that obviously very closely," Slotter told reporters. "We have not reached the point where we can say the two were connected ... I think we're way ahead of the game to characterize something like this as a serial bomber."

More than one pipe bomb, it's unclear how many, were left outside the federal courthouse Sunday shortly before they exploded around 1:40 a.m., causing "considerable damage" to the entrance and lobby, Slotter said.

Debris was found lodged in a window about eight stories up the AT&T building across the street. The courthouse is located near the Gaslamp Quarter's bars and nightclubs.

"This was a pretty powerful bomb," Slotter said.

The courthouse was scheduled to reopen Tuesday, said Mark Owen, acting chief deputy of the U.S. Marshals Office for the Southern District of California. There was no estimate of property damage.

About 40 investigators are working on the case and federal authorities are treating it as a top priority, Slotter said.

Evidence was flown Monday to FBI labs in Quantico, Va.

Slotter said the motive for the attack was unclear.

"Is it (someone) trying to make a statement to the government? To the justice system?" he said. "Who knows?"