Federal prosecutors and Nashville police on Saturday said they are following more than 500 leads and tips in their investigation into an explosion that rocked downtown Nashville, Tennessee, on Christmas morning.

The big picture: The explosion, which injured at least three people, caused widespread telephone, internet and other outages in central Tennessee and in parts of neighboring states. Governor Bill Lee said on Saturday that he has asked President Trump for federal assistance in the state's relief efforts.

• The White House did not immediately respond to Axios' request for comment, but a spokesperson previously said that Trump had been briefed on the incident.

Before Friday's explosion, witnesses reportedly heard a voice from the RV, saying, "Evacuate now. There is a bomb. A bomb is in this vehicle and will explode." 

• The voice then started a 15-minute countdown and playing music.
• Officers, responding to an early morning call on Friday for shots fired, encountered the RV as the recording played, police said. The officers began evacuating nearby buildings.
• The RV exploded around 6:30 a.m. CT, according to authorities.
• Lee said preliminary reports show at least 41 buildings and businesses were damaged.

What they're saying: "We will get to the bottom of this [and] we will find out the story of this individual or individuals ... of this ultimate Scrooge, who on Christmas morning instead of spreading joy and cheer, decided to spread devastation and destruction," U.S. attorney Donald Cochran said Saturday afternoon.

• Nashville Metro Police Chief John Drake added that "Nashville is safe. We feel and know that we have no known threats at this time."
• Gov. Lee tweeted after visiting the site of the explosion said that the "damage is shocking and it is a miracle that no residents were killed."