Investigators on Monday were hunting for a motive behind the Christmas morning blast that shook downtown Nashville, taking the life of the bomber and leaving behind a tangle of debris and questions.

The fiery boom, which was foreshadowed by a countdown clock warning of the explosion to come, did extensive damage to nearby shops, severed communications in multiple states and injured three people.

Authorities say it also incinerated the bomber, identified as 63-year-old Anthony Quinn Warner, a tech worker and recluse who did not appear to have left behind any explanation for his actions. Law enforcement officials acknowledged Monday that they may never know for sure what motivated him.

“We hope to get an answer. Sometimes it’s just not possible,” said Tennessee Bureau of Investigation Director David Rausch. “The best way to find motive is to talk to the individual. We will not be able to do that in this case.”

But even without an interview, there have been some early clues: Investigators are pursuing the possibility that distrust of 5G technology — and phone service in general — played a role in his thinking.

Warner’s explosives-packed recreational vehicle was parked near an AT&T communications hub when it detonated. Conspiracy theories about 5G technology have proliferated online this year, with people trading unfounded claims that the relatively new system for mobile communication is also spreading the novel coronavirus.

But authorities said they have also gathered evidence suggesting Warner’s interest in other unusual subjects, according to two people familiar with the investigation. They cautioned that someone who commits such an irrational act may not have a rational reason for doing so, and emphasized that the inquiry is just getting started.

“We’re at the beginning stages of determining the motive,” said FBI Special Agent Jason Pack. “It could be weeks before we have a comprehensive picture.”

Agents from the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives were among the investigators in hard hats on Monday combing through debris at the blast site. Authorities said evidence had been sent to Quantico, Va., and the FBI is analyzing it to determine what substance was used to cause the explosion.

The explosion, and Warner’s role in it, stunned neighbors in Antioch, a middle-class suburb of brick, single-family ranches and duplexes where he had lived a quiet life, seemingly disconnected from others. Residents of his street said he seemed obsessed with home security and had multiple cameras positioned on his property.

One longtime neighbor, Rick Laude, said Warner kept to himself and never initiated contact. But he said he had visited Warner’s house a week ago to offer Christmas greetings.

“I asked him, ‘Is Santa going to bring you anything good for Christmas?’ ” recounted Laude, a 57-year-old truck driver. “He just smiled and said, ‘Oh yeah. I'm going to be famous. Nashville and the world are never going to forget me.’ ”

At the time, Laude said he interpreted the comment to mean that something positive was coming in Warner’s life: Laude knew that Warner worked in information technology. Maybe he had sold an app that would make him rich and famous?

The potentially darker implications only came into focus on Sunday, after authorities identified Warner as the bomber and said that human remains from the scene had matched Warner's DNA.

President Trump had not publicly commented on the incident as of Monday afternoon, though the White House released a brief statement on Friday saying the president is “grateful for the incredible first responders and praying for those who were injured.”

Tennessee Gov. Bill Lee (R) told Fox News on Monday that he had spoken with Trump and that an emergency declaration would be forthcoming to help the state cover the cost of rebuilding, as Lee had requested.

“We’re very grateful to President Trump for his response to that request,” Lee said.

President-elect Joe Biden on Monday called the explosion “a reminder of the destructive power that an individual or a small group can muster, and the need for continuing vigilance across the board.”

Biden praised the police officers and others who responded to the reports on Christmas morning of a suspicious vehicle, particularly the five officers who evacuated the area as a loudspeaker in the RV gave a 15-minute countdown to detonation.

“Their bravery and coolheadedness likely saved lives and prevented a worse outcome, and we are eternally grateful,” he said.

Metro Nashville Police released a nearly 13-minute video from a body camera worn by one of the officers, Michael Sipos, who was on the scene in the minutes before the blast.

“That’s so weird,” an officer can be heard saying as the recording from the RV repeats.

“Do not approach the vehicle,” the recording says. “Your primary objective is to evacuate.”

Rausch, Tennessee’s top investigative official, said the existence of the countdown suggested that Warner’s “intent was more destruction than death.”

“The opportunity to clear the area certainly gives you that insight that the possibility was that he had no intention of harming anyone but himself,” Rausch said in a Monday morning interview on NBC’s “Today.”

In a later appearance with reporters, Rausch said that Warner had not been known to the Tennessee Bureau of Investigation before the explosion.

“He was not on our radar,” Rausch said.

Warner’s criminal record in Tennessee was scant: an arrest for marijuana possession in 1978.

Rausch said his bureau’s agents are working with police, the FBI and ATF and are interviewing people who knew Warner, including relatives and neighbors.

“We are all taking pieces of the puzzle, working to determine what the motivation was for this individual,” he said.

One of those pieces could be Warner’s father, who worked for AT&T or one of its subsidiaries. Rausch said that interviews “are still being conducted to determine if that plays in whatsoever in the motive. At this point it’s all speculation.”

Warner’s father died in 2011. Warner himself had worked as a computer consultant for a local real estate company for 15 years, before retiring this month.

Long before that, he had worked for an alarm company.

“He was just a smart, quiet guy that didn’t like the police,” said Tom Lundborg, who worked with Warner four decades ago at what was then A.C.E. Alarms, a company Lundborg’s father started in 1968. “He was kind of a hippie, with long hair. Just was a nice-looking guy.”

Lundborg recalled that it briefly angered his family when Warner left A.C.E. Alarms to start his own company, which he said was called Custom Alarms.

“But he didn’t do very well,” Lundborg said. “He’s technically proficient but didn’t have the people skills.”

Should paranoia over 5G prove to have been part of Warner’s motivation, it would mark the highest-profile attack to date borne of conspiracy theories surrounding the technology.

Already, 5G towers have been burned and workers have been stalked or threatened by people who blame the technology for the spread of the coronavirus, as well as other ills.

While the theories have no basis in fact, they have gained prevalence this year as communication companies roll out service and as the virus continues its spread, said Imran Ahmed, chief executive of the Center for Countering Digital Hate.

“Think about what 5G and covid are. They’re novel, they’re relatively unknown and they’ve been promoted as game changers,” Ahmed said.

Previous generations of technology, including 3G and 4G, have been blamed in dark corners of the Internet for other disease outbreaks.

The myth of a link this time, Ahmed said, has been especially potent because “covid is so lethal and it’s changed our lives in such profound ways. It drives the interest” in these conspiracy theories.

 Michael Kranish, Julie Tate, Jennifer Jenkins and Isaac Stanley-Becker contributed to this report.