FBI training prepares investigators for bombing probe

13 Investigates went behind the scenes with the FBI for an exclusive look at bomb training at Fort Nellis.

The FBI has warned about the threat of domestic bombings well before Monday's blast in Boston.

In fact, 13 Investigates went behind the scenes with the FBI for an exclusive look at bomb training at Fort Nellis. Now those days in the desert are preparing investigators for a range of scenarios.

Hidden in the rugged terrain of a Nevada desert, improvised explosive devices are set off by remote control.

"Fire in the hole! Fire in the hole! Fire in the hole!," yelled an FBI trainer before 13 Investigates pushed the code to ignite 200 pounds of explosives packed into a van more than two football fields away.

Homeland Security teams from all across the country were there too, getting firsthand training from the FBI on how the bombs are made, what happens when they explode and where to look for investigative clues.

13 Investigates was the only Indianapolis television station allowed in the danger zone.

The FBI was trying to get ahead of its growing intelligence on potential domestic terror.

That was 2008, nearly five years ago.

"Resources are limited so what we hope to do is expand the information network -- the intelligence network throughout the United States," explained Jeff Muller of the FBI.

It's that kind of training investigators are now relying upon in the face of the Boston Marathon bombing.

Already they have tracked down some key components, including a six-liter pressure cooker and shrapnel. The injuries of those maimed reveal ball bearings were also added to the mix.

Now it's up to forensic testing to reveal the bombs' DNA, specifically the mix of chemicals used to create the improvised explosive device.

"The term IED is a broad umbrella term for any kind of explosive device that's made in an improvised fashion, made by a non-expert for purposes of harming other people," explained John Goodpasture of IUPUI.

Goodpasture says it appears the blast strength of the explosives were high in Boston, the surge of power too fast to ignite a fire.

In the Nevada desert, a range of test bombs, from small amounts of highly concentrated explosives, to those packed with more hundreds of pounds of material. All of it training for a "what if" this is now an unfortunate reality.

Federal agents in Boston are reportedly making significant progress. They have identified two men they want to talk to seen in crime scene video and they visited several Boston area Hobby stores to pinpoint where electrical components used to build the bombs may have been purchased.