More than 50 years after a bombing at the University of Wisconsin left one student dead, the FBI has released age-progressed photos of the suspect in its quest for more tips from the public.

Leo Frederick Burt, who was 22 at the time and now in his 70s, is wanted for his role in the Aug. 24, 1970, bombing of the University of Wisconsin's Sterling Hall, which was intended to destroy the Army Mathematics Research Center at the school in protest of the Vietnam War.

"The blast from the explosion, combined with the fire, resulted in the death of a 33-year-old researcher. Additionally, there were several injuries reported and an estimated $6 million damage to the building and its contents," the FBI said in a recently updated wanted poster for Burt. "Reportedly, explosives had been placed in a stolen panel truck, located three blocks from the building, just several days before the blast."

In a 2010 press release offering a $150,000 reward for Burt's arrest, the FBI described the bombing as "the largest act of domestic terrorism in U.S. history" at the time "until the Oklahoma City bombing 25 years later."

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A photo of Leo Frederick Burt from 1969 compared to two new age-progressed photos of Burt

Leo Frederick Burt, who was 22 at the time and now in his 70s, is wanted for his role in the Aug. 24, 1970, bombing of Sterling Hall at the University of Wisconsin, which was intended to destroy the Army Mathematics Research Center at the school in protest of the Vietnam War. (FBI)

Burt was identified as being one of the passengers in a light-colored Chevrolet Corvair seen leaving the vicinity of the university bombing, the FBI said. Three other suspects – Karleton Armstrong, Dwight Armstrong and David Fine – were arrested in connection with the attack. The group called themselves the "New Year’s Gang."

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Burt, an aspiring journalist who also went by the alias Eugene Donald Fieldston, has yet to be captured 53 years later.

Leaving police headquarters today for his extradition hearing, Karleton Armstrong is led by Constable Ken Greer. Armstrong is wanted in Wisconsin in bombing of a university building in which a scientist was killed.

Karleton Armstrong, Dwight Armstrong and David Fine were arrested in connection with the bombing. The group called themselves the "New Year’s Gang." (Don Dutton/Toronto Star)

Scott Decker, the former FBI special agent on the investigation into the 2001 anthrax attacks, likened Burt and his alleged crimes to those of the Weather Underground – a far-left militant organization that was active in the 1970s.

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"Back in the early 70s, you caught a lot of these characters – the Weather Underground. [Burt] wasn't named as the Weather Underground, but there are a lot of similarities between what he did and … what the Weather Underground was doing across the country," Decker told Fox News Digital. "The bombings and even the use of fake IDs."

The Sterling Hall Physics building on the University of Wisconsin's campus which houses the Army Match Research Center stands shattered after an apparent bomb exploded inside the building after the Aug. 24, 1970, bombing.

A 33-year-old researcher was killed in the Aug. 24, 1970, University of Wisconsin bombing staged in protest of the Vietnam War. (Getty Images)

Decker further explained that the FBI likely released new age-progression photos of Burt in an effort to bring renewed light to the case and seek more help from the public. The agency caught Whitey Bulger – the Boston organized crime boss who inspired the movie "Black Mass" – in California in 2011 after releasing an age-progressed photo of what he might have looked like in 2004, the former FBI special agent said.

"I think the age progression on this is pretty reliable. So, it'll definitely generate phone calls. I'm sure if they can get it on 'America's Most Wanted' on TV … it'll bring it back into the public eye and with a picture of what he looks like now, if he's in a shelter or if he's a security guard somewhere, it's very likely to generate a phone call. And so Whitey Bulger was caught."

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Burt was federally indicted in Madison, Wisconsin, less than 10 days after the bombing on Sept. 2, 1970, and charged with sabotage, destruction of government property, and conspiracy. He has been considered a fugitive ever since.

An aerial view of the Sterling Building following the University of Wisconsin bombing in 1970

The University of Wisconsin bombing left one person dead, others injured and caused millions of dollars in damage. (FBI)

Possible Burt sightings have been reported everywhere from a homeless encampment in Denver to a resort in Costa Rica, according to the FBI. He has ties to New York City, Boston, and Peterborough in Ontario, Canada.

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Retired Special Agent Kent Miller, who led the search for Burt for several years, said in 2010 that he doesn't believe the fugitive is still living in the United States.

"I don’t think he’s living in the United States. And if he is alive," Miller said, "he’s got to be worried every day that he’s going to slip up and get caught. That’s no way to live."