Nearly 30 years ago, Ret. FBI Special Agent Barry Black responded to the worst homegrown terrorist attack in U.S. history with just a year of experience as a bomb technician under his belt.

Black was one of two FBI bomb techs in the entire state of Oklahoma, including Jim Norman, when he arrived at the Alfred P. Murrah Federal Building, which housed offices for approximately 500 government employees, around 9:30 on April 19, 1995. Nearly half an hour earlier, at 9:02, ex-Army soldier Timothy McVeigh ignited a bomb that took a third of the nine-floor building, killing 168 victims.

“It was horrific and chaotic. The scope and magnitude of the destruction was something like I had never seen before,” Black told Fox News Digital of his memories of the attack 29 years later. “{I’ve] sadly seen similar since. But other than the first World Trade Center attack, the U.S. had not seen an attack like this.”

Black’s responsibility as a bomb tech was to “assess the scene,” he said.

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“We were told maybe it was an airplane crash or a gas main explosion. Clearly it was not. And … the scale was something that few had seen in this country,” the former special agent said.

The explosion registered a 6.0 on the Richter scale and was felt an estimated 55 miles from the scene, according to the Justice Department. It left cars upturned and damaged more than 320 nearby buildings.

Among the 168 who perished in the attack, 19 were children, as the Murrah building housed a daycare on the second floor. The last of the deceased was a nurse who had been responding to the emergency when a piece of falling debris struck and killed her.

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Black went into the building every week to pick up a paper paycheck. The tellers who handed him that paycheck every week “were all killed,” Black recalled.

His wife, a federal probation officer, was also in the building that morning, but she drove out at 9 a.m., two minutes before the explosion.

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“I have been to a number of these catastrophic events. What makes this a little different is: this was in my backyard. These were people I knew. My wife was in the building. At 9:00, she drove out — two minutes before the detonation — and it was about an hour and a half before I knew she was OK,” Black recalled.

When he arrived, “the devastation was overwhelming,” he said.

“But as I did what we call the initial survey — kind of a walkabout to try to assess the damage and get a handle on what may or may not have occurred — I asked some of the security people … if they’d seen my wife, and I recall one specifically said, ‘Yep, I’ve seen her and she’s fine.’ Well, that sort of freed me up. He later told me that he had not. He just thought I needed to hear that she was OK. So, good, bad or indifferent, that’s what he told me. And it took a little of the load off.”

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While sorting through rubble for evidence a day after the attack, investigators came across the rear axle of a Ryder rental truck used to detonate the bomb with an identification number on it.

“That morning, a reserve deputy called myself and the other bomb tech, Jim Norman, to that rear … axle, and he wiped away some grease, and we wrote down that CBI and then physically gave it to a runner who … took it to the command post,” Black recalled. 

From there, investigators were able to track down the fake name McVeigh used to rent the vehicle, and employees at the rental shop were able to help investigators put together a composite sketch of their suspect. Once the sketch was released to the public, a hotel employee in Junction City, Kansas, identified the suspect as 27-year-old McVeigh.

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By April 21, authorities learned McVeigh was already in jail after a state trooper pulled him over about 80 miles north of Oklahoma City, just 90 minutes after the bombing, for a missing license plate, according to the FBI. He had a concealed weapon on him at the time and was detained.

Later on, federal agents found evidence of the chemicals used for the bomb on McVeigh’s clothing and a business card on which he had written, “TNT @ $5/stick, need more,” according to the FBI. Authorities also arrested Terry Nichols, who helped McVeigh make the deadly bomb.

Following 28,000 interviews that were conducted across the world, investigators were able to piece together McVeigh’s and Nichols’ motives for the horrific act: They were angry about the April 19, 1993, Waco siege, as well as the August 1992 siege at Ruby Ridge, according to the FBI and DOJ.

“I’m confident we know his motivation. It was intended to be the first blow in an upheaval and overthrow of the federal government,” Black said. “Intent is one of those things that’s intangible but required to prove. So there was a great deal of time spent looking into why he would do this. And the same is true whether it’s domestic or international terrorism. But his motivation was proven clearly.”

Black said lessons from the FBI’s investigation into the Oklahoma City bombing are still relevant today, and those lessons are part of what he teaches as a professor at the University of Central Oklahoma Forensic Science Institute.

“There are specific things we would look for on scene, like parts of the bomb, parts of the vehicle that carried the bomb. And that information needs to get relayed quickly to the command post so that the larger, broader external investigation can begin. And that’s how we had McVeigh and Nichols in custody in about 54 hours after detonation,” Black explained. “It was a massive undertaking with law enforcement work[ing] very, very well together.”

McVeigh was executed in 2001 at age 33.