Investigators have not identified the victim, nor have they offered any details about what exploded.
"It would be premature to be speculative on what the explosive device is right now," said FBI spokesperson Kevin Rowson.
On Monday, the FBI opened an investigation into the death and explosion. Beyond no suspicion of terrorism, there are few details and plenty of questions.
"We know where it happened, right where the individual was deceased. What he was doing between those two buildings, at that point, at 1:30 in the morning on Sunday, we don't know at this point," Rowson said.
Evidence has already headed to the FBI crime lab in Quantico, Virginia, and by 2:30 p.m. Monday, the bureau's evidence response team set up another barrier.
Some of the focus was on the U-Haul truck.
Even though we've seen law enforcement officers going in and out of the complex all day, neighbors are not having any issues getting to their homes.
FBI Atlanta is asking for anyone with information about this man's identity or the explosion to contact them directly.