A Minnesota man who claimed to build special effects for the NFL and Hollywood movies, including the blockbuster "Transformers" franchise, pleaded guilty in federal court Tuesday to illegally manufacturing and selling explosives.

Federal agents raided the Brownsville, Minn., home of Kenneth Miller, 58, in March, following a 10-month investigation that started with a profile in Popular Science magazine on Miller's pyrotechnic work. The magazine article included photographs of Miller shooting red flares off the hood of his pickup truck and packing powdered chemicals in a nearby shack he used as a makeshift laboratory.

"His personal pyrotechnic experiments don't belong on the 50-yard-line or in anyone's backyard," reads the article, which came across the desk of a special agent for the Bureau of Alcohol, Tobacco, Firearms and Explosives in May 2019.

Investigators learned Miller's felony convictions precluded him from touching the highly combustible material used to create these devices. In his plea, Miller admitted to manufacturing and selling smoke-generating devices and a chlorate explosive mixture to customers across the country from 2013 to March 3.

Miller was first convicted of a felony for conspiracy to make illegal explosives in 1986. A few years later, he was convicted of illegally possessing a firearm in North Dakota.

In 2004, investigators from the Houston County Sheriff's Department visited Miller after an anonymous tip that he'd been making fireworks. The officer found red powder residue and 55-gallon drums labeled "Pyrotech," the name of his company, on his property, according to police reports. At the time, Miller told agents he used legal chemicals to make flares and smoke bombs.

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Ken Miller

By the time the ATF called, the sheriff's office said they were "very familiar" with Miller's work building explosives from community complaints and reports of fireworks and flares flying above the tree line. Last year, the Department of Natural Resources came to investigate a wildfire in the state forest surrounding Miller's home.

Miller first denied knowing anything about how the fire started, according to incident reports. After investigators found parachutes in the trees, Miller admitted that his teenage son was shooting off a 12-gauge flare gun he'd been preparing for a customer.

Miller also faced a lawsuit in 2011 from a customer claiming one of his devices blew the man "from his feet and onto his back, and blew shrapnel through and into his eye," leaving him with one eye.

In 2000, the ATF investigated an explosion in North Dakota involving Miller and a man named Howard Snelson. Miller had been left badly burned. Snelson "died as a result of the explosion due to smoke inhalation and thermal burns," according to a warrant unsealed earlier this year. Miller had told police Snelson was his best friend and business partner.

When ATF agents arrested Miller in March, they also found firearms on his property, which Miller is prohibited from possessing due to his felonies, according to the federal complaint. Those charges have since been dropped, and Miller pleaded guilty to the single explosives count in front of Judge Patrick J. Schiltz in U.S. District Court in Minneapolis Tuesday. His sentencing has not yet been scheduled.

Andy Mannix • 612-673-4036