A 43-year-old Houston man pleaded not guilty Thursday to federal firearms violations including illegally possessing a bump stock, the first such case in the U.S. since the Department of Justice outlawed possession of the devices in March.

The brief arraignment follows the Sept. 4 indictment of Ajay Dhingra on four firearm violations, including possession of a machine gun, lying to obtain firearms, and illegally possessing a firearm. If convicted, Dhingra could face up to 10 years in federal prison and a $250,000 fine on each count.

“We’re looking into the evidence and the accusations against Mr. Dhingra,” said David Adler, his attorney.

Dhingra was first arrested Aug. 17. He is being held in a federal detention center in Houston, prison records show.

Federal court records show authorities began investigating Dhingra after he sent an email to the George W. Bush Foundation asking the former president “to send one of your boys to come and murder me,” and said he wanted to “die by the hands of a dirty white Christian.”

Investigating agents interviewed Dhingra’s relatives and discovered he had been diagnosed with schizophrenia and committed to a psychiatric facility -- which would prevent him from legally possessing firearms. Dhingra’s mother and brother told investigators he refuses to take his medication.

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Despite that, Dhingra had obtained a concealed carry license, according to federal court records, and investigators discovered that he owned a Glock 43 and an AR-15 outfitted with a Slide Fire bump stock, along with four 100-round magazines.

Bump stocks replace a rifle’s typical stock and “bump” between a shooter’s shoulder and trigger finger, causing the rifle to fire far more quickly than a shooter might without the device. The speeds mirror those of automatic weapons.

Interest in the devices -- and controversy -- surged after the 2017 Las Vegas massacre, when a gunman holed up in a hotel with a dozen rifles equipped with bump stocks used them to kill 58 people and wound hundreds of others.

The Bureau of Alcohol, Tobacco, Firearms and Explosives ruled in 2010 that bump stocks did not convert semi-automatic rifles into machine guns, which federal law prohibits most people from possessing. After the October 2017 Las Vegas massacre and the Parkland shooting several months later, President Donald Trump ordered a rule banning the devices, and the federal government subsequently redefined machine guns to include bump stocks.

When prosecutors first announced Dhingra’s indictment, they said ATF officials identified it as the first bump stock court case filed by the Justice Department.

Court records show Dhingra told investigators he believed he was autistic, and that he said he bought his firearms in 2016 after a mass shooting in Florida that claimed 49 lives.

Experts said the case served as a warning to the hundreds of thousands of people who have purchased the devices over the last decade.

“It is evident that the government was serious and felt bump stocks were as lethal as machine guns, as we saw in Las Vegas,” said David Chipman, a former ATF agent and adviser with Giffords, a gun-control advocacy group. “This is a warning to put people on notice that if they have bump stocks, they need to turn them in or destroy them.”

But the case could have implications on the government’s new rule outlawing the devices, said Josh Blackman, a constitutional law expert and associate professor at South Texas College of Law Houston.

“This case may present a better vehicle to challenge the Trump rule,” Blackman said.

Across the country, several people have sued the federal government over the ban, Blackman said, though the Supreme Court in March refused to block the ban from going into effect.

“The Trump administration reinterpreted the definition of automatic weapons and say the bump stock is covered by the statute,” he said. “My read of statute is that bump stock does not violate National Firearms Act.”

If defense attorneys successfully challenge the validity of the ban, that would have “nationwide scope,” he said.

st.john.smith@chron.com