Updated 2:37 p.m.

One day after a Christmas bombing in downtown Nashville damaged dozens of buildings over several blocks, police are working with federal authorities to find the perpetrator.

"This morning I toured the site of the bombing," Tennessee Gov. Bill Lee said on Twitter on Saturday. "The damage is shocking and it is a miracle that no residents were killed."

In a letter asking President Trump for federal assistance, the governor noted that the blast affected more than 20 local 911 call centers, residential phone lines and cell service.

A White House spokesman said Friday morning that President Trump was briefed on the explosion, and was "grateful for the incredible first responders and praying for those who were injured." But as of Saturday afternoon, the president himself had made no mention of the blast on his Twitter feed.

Law enforcement has received more than 500 leads and tips, and investigators are combing through the wreckage for clues. "It's like a giant jigsaw puzzle created by a bomb that throws pieces of evidence across multiple city blocks," said U.S. Attorney Don Cochran an a news conference on Saturday.

Cochran said he was confident investigators would find the culprit, who he described as "this ultimate scrooge who on Christmas morning, instead of spreading joy and cheer, decided to spread devastation and destruction."

Large portions of the state's communications networks remained out of service Saturday, the Associated Press reported. In his request for an emergency declaration, Lee said communications were impacted as far away as Kentucky and northern Alabama.

The blast occurred early Friday morning, hours after an RV was parked in front an AT&T building on Second Ave., a popular strip of honky-tonk bars and restaurants. A few hours after the RV appeared around 1 a.m. CT, a recorded voice warned that the vehicle was going to explode, and police went door-to-door to evacuate residents. Around 6:30 a.m., the vehicle exploded, knocking out communications and disrupting local flight control systems, briefly grounding flights at the Nashville International Airport.

Now, local police are working with the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives to determine who was responsible.

Hundreds of FBI agents, analysts and staff are on the ground in Nashville, said Douglas Korneski, FBI special agent in charge of the Memphis field office. The behavioral analysis unit in Quantico, Va., is also on the case. Investigators aren't sure if it was one person acting alone, or multiple suspects, but there are "a number of individuals we are looking at," Korneski said.

"Federal agents have poured into downtown to look for pieces of the RV and any other evidence," NPR's John Burnett told Weekend Edition. "They're reviewing videos from security cameras and they've asked the public for leads."

At least 41 separate businesses were "materially damaged" by the blast, and several downtown residents' homes were destroyed, Nashville Mayor John Cooper said at a Friday evening press conference. Shockwaves from the blast could reportedly be felt from miles away. Three people hospitalized as a result of the explosion were in stable condition Friday night. No fatalities were reported.

It's not clear if anyone was inside the vehicle when it exploded. Metro Nashville Police Chief John Drake says human tissue may have been found at the scene, NPR member station WPLN reports.

The RV explosion, which authorities described as an "intentional act," damaged an AT&T building that housed telecom equipment and also knocked out power to the building. Crews were working on restoring power Saturday morning — a task made difficult by the ongoing aftermath of the explosion, such as a fire that reignited overnight and forced the building to be evacuated.

"The blast caused injuries and catastrophic damage to this very historic part of Nashville," Cooper said. "I think all of us — I certainly have — have gone from relief that there were not more casualties ... to now anger and determination and resolve, and a resolve to rebuild, and not to be deterred, and to bring whoever was responsible for this to justice."

AT&T said Saturday morning its teams were on site, working with safety and structural engineers to restore service.

"They have drilled access holes into the building and are attempting to reconnect power to critical equipment," the company said in a statement. "Technical teams are also working as quickly as possible on rerouting additional services to other facilities in the region to restore service."

Cooper declared an emergency in the area, and imposed a curfew there to extend through Sunday afternoon. But it will be some time before 2nd Ave. in downtown Nashville is back to normal, Cooper said. "Our partners at the FBI do have a large crime scene to investigate."

The FBI has asked anyone with information to contact them on their web site.

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