Authorities have found possible human remains in the area where a Friday morning explosion rocked downtown Nashville and injured three people, an event police called “an intentional act” connected to an RV that blew up at approximately 6:30 a.m. local time.

It was unclear whether the remains were related to the explosion or if they were of the person responsible or a victim, officials said. The tissue will be examined, officials said. The FBI is investigating along with local officials and the Bureau of Alcohol, Tobacco, Firearms and Explosives, and the city of Nashville activated its Emergency Operations Center.

“This appears to have been an intentional act,” Metro Nashville Police Department tweeted. “Law enforcement is closing downtown streets as investigation continues.”

An audio warning was being broadcast from an RV just before it blew up, Metro Nashville Police Department Chief John Drake told reporters during a news conference.  

“If you can hear this message, evacuate now,” the warning said. 

Officers first responded to the area after receiving a report of shots fired, Drake said. They called in the bomb squad after seeing the suspicious vehicle, the RV, broadcasting the message, he said. Drake said that officers found the RV with a recording saying that it would explode in 15 minutes.

“Basically (it) was saying that it was going to detonate within a certain time frame,” Drake told reporters. “The officers immediately began knocking on doors and evacuating residents here not knowing if the bomb was going to detonate immediately or if it was going to go off in the time that it stated.”

As of late Friday evening, police did not know if anyone had been inside the vehicle at the time of the explosion.

Three people suffered injuries related to the blast and were in stable condition, Mayor John Cooper said. In addition, 41-area businesses and several homes sustained damage. Several residents were displaced, fire Chief William Swann said. 

The American Red Cross of Tennessee said was assisting displaced victims.

Drake praised the actions of the six officers, saying if it were not for them, “we’d be talking not about the debris that we have here but also maybe potential people.”

He said investigators haven’t determined a motive for the explosion. He initially thought the incident was a propane explosion instead of an “intentional act,” he said. 

The investigation is now being led by the FBI’s Memphis field office, and a spokesperson for the Department of Justice said Acting Attorney General Jeff Rosen “directed that all DOJ resources be made available to assist in the investigation.”

VEHICLE PLAYED RECORDING SAYING BOMB WOULD DETONATE, UNKNOWN IF SOMEONE INSIDE RV: POLICE

“We’re putting everything we have into finding who was responsible for what’s happened here today,” FBI Assistant Special Agent in Charge Matt Foster told reporters during a Friday afternoon news conference. Drake told reporters at that time that he and his department “don’t feel there’s any concern to the downtown area” anymore.

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