NASHVILLE, Tenn. (WTVF) — A retired ATF investigator said the downtown bomb could've been built with materials anyone can buy.
The investigator, who retired from the ATF less than a year ago, said his theory is the bomb was, at least in part, made out of pyrotechnics.
David Hyche spent 31 years at the ATF. He is an explosives expert and spent much of his career doing post-explosion investigations.
"I also saw what appeared to be some solid material that was burning," said Hyche. "That makes me think there's a reasonable chance this is a pyrotechnic mixture similar to what's in commercial fireworks. The two main components for a pyrotechnic mixture can be purchased legally without any sort of background check or anything else."
Hyche is now the chief of police of Calera Police Department in Alabama. He's able to speak about his expertise in regards to this explosion because he is no longer directly involved with the ATF or this investigation.
He said it doesn't appear the bomb was a manufactured explosive, but instead contained various fuel, which is why there was a large fireball.
"The duration of the thermal event, or how long it took for the fuel to be consumed, all explosives are fuel and an oxidizer," said Hyche. "There's a lot of fuel in this explosion. I don't know what type of explosion, I have a theory but it's a long thermal event. A high explosive will typically happen in an instant. The energy, the fuel and the oxidizer are at such a balance that it's consumed almost instantaneously."
Hyche said debris from the blast seen landing in the Cumberland River will almost certainly be looked into by investigators if it hasn't already.
He said it's likely the ATF and FBI have video the public has not seen yet.
"They'll take a look at it frame by frame and look at it. They'll use that to help them in their search patterns. They've already done most all of this anyways," said Hyche.