The man believed to be the mastermind of the Christmas Day bombing in downtown Nashville killed himself in the blast and appears to have been working alone, ABC News and others reported Monday.

Authorities said state and federal investigators matched DNA and other evidence from the scene to items collected from 63-year old suspect Anthony Q. Warner and his relatives.

Douglas Korenski, special agent in charge of the Federal Bureau of Investigation's Memphis field office, said close-circuit television obtained showed no one else was seen around the recreational vehicle at the time of the explosion.

"Anthony Warner is the bomber. He was present when the bomb went off and he died in the explosion," USA Today quoted U.S. Attorney Donald Cochran saying.

No motive was given by authorities nor was it disclosed why Warner had chosen the particular spot for the bombing which destroyed an AT&T building and has continued to disrupt cell phone service and police and hospital communications in many Southern states.

In a statement Sunday, AT&T said it had restored power to many floors of the building and deployed 25 temporary cellular satellite towers to the city.

After the bombing, Metro Nashville Police chief John Drake said "Nashville is considered safe... there are no known threats against this city."

Warner, whose public records show worked as a computer consultant for a real estate agent in Nashville and had experience with electronics, wasn't known to law enforcement before the explosion, police said.

The types of explosives Warner used were being examined, police said. The FBI declined to call the bombing an "act of terrorism."

In other news, three people were killed while three others were wounded when an active-duty U.S. Army Special Forces sergeant allegedly opened fire at a bowling alley in Rockford, Illinois, late Saturday, authorities said.

Winnebago County State Attorney J. Hanley said 37-year old Duke Webb has been charged with three counts of murder and three counts of first-degree attempted murder.

According to Rockford Police director Dan O'Shea, they believe the shooting was "a completely random act" and there was no prior meeting or any kind of relationship between Webb and any of the victims.