On Sunday, the FBI said there was no indication of additional suspects involved and that it was too early to suggest a motive.
The blast outside a telecoms office disrupted communications systems in Tennessee and four other states.
Officers responded to reports of gunshots just before 06:00 local time (12:00 GMT) on 25 December in an area of the city known for its restaurants and nightlife.
Shortly afterwards, they found a camper van broadcasting a warning message to leave the area.
Police said the van had also broadcast the 1964 hit song Downtown by British singer Petula Clark, the Tennessean newspaper reported.
The van exploded a few minutes later, the force of the blast knocking an officer off their feet, police said.
The vehicle blew up outside a building belonging to the telecoms giant AT&T, which also occupies an office tower nearby.
Buildings suffered structural damage, windows were blown out, and trees were felled. Videos posted on social media showed water from damaged pipes running down walls as alarms howled in the background.
Police emergency systems were knocked out across Tennessee. Telephone, internet and fibre optic TV services were also disrupted in Tennessee, Mississippi, Kentucky, Alabama and Georgia, according to AT&T.
Police later released this image of the van arriving at the scene early on Friday.
During a press conference on Sunday, federal investigators said they believed that Warner, who worked in IT and had extensive experience with electronics, was the sole individual responsible for the blast and had died at the site.
They said the blast was probably deliberate, and that it was Warner's remains discovered at the scene.
"We're still following leads but right now there is no indication that any other persons were involved," said FBI Special Agent in Charge Douglas Korneski.
Police also released footage of the moment the explosion took place.
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