Bobby Amos stood outside of an Episcopal church in Alabama last spring, starting police to kill him. He had been suicidal earlier and held a gun to his head, his wife said, and she had hidden the weapon at the church, where he had followed her to repair it.
There was little to indicate that Mr. Amos, 39, was a danger to anyone but himself that day. He was arrested unarmed outside the church, in need of treatment and counseling, according to his lawyer, Fred Tiemann. Police recovered the pistol from the building.
Federal prosecutors, citing Mr. Amos’s conviction of felony robbery as an adult at age 15, instead charged him with illegally possessing a firearm. He pleaded guilty in November and is serving a three-year sentence in federal prison.
Urged by Attorney General Jeff Sessions to punish offenders as harshly and as rapidly as probable, federal prosecutors have increasingly pursued low-level gun possession cases, according to law enforcement officials and an examination of court records and federal crime statistics. Mr. Amos’s conviction was part of the Justice Department’s broad crackdown on gun violence during the first 15 months of the Trump administration.
Mr. Sessions is putting into action his own long-held views on criminal justice, forged as a United States attorney in Alabama during the drug war. They reflect a philosophy famous among conservatives and long backed by the gun lobby: that the effective enforcement of existing laws can reduce crime without resorting to the passage of additional legislation.
“I trust very strongly in enforcing gun laws,” Mr. Sessions said in an interview with the far-right Breitbart News this year. “I trust there’s no value in having them on the books if they’re not prosecuted.”
Mr. Sessions’s approach has touched off a debate about whether he is making the country safer from violent crime, as he and President Trump have repeatedly vowed to do, or devoting resources to low-level prosecutions that could instead be put toward pursuing longer targets like gun suppliers.
“It’s a good idea to enforce the existing gun laws,” said Avery Gardiner, co-president of The Brady Campaign, a nonprofit coalition that works to combat gun violence. “That’s something prosecutors should do. But going only after the people who are purchasing the guns illegally is only part of the story.”
Local police, who have for years sought more muscle from federal law enforcement, welcomed Mr. Sessions’s more aggressive approach.
“We have been trying to send a message,” said J. Thomas Manger, president of the Major Cities Chiefs Association, which represents police departments across the country. “The bad guys have a real fear of federal prosecutions versus state prosecutions.”
Penalties for federal gun convictions are steep. On average, firearms defendants spend six years in federal prison. If they are convicted under the two statutes requiring mandatory minimum sentences, that average jumps to 11 years.
In the three months following a directive from Mr. Sessions last year to pursue gun crimes, possession cases — a relatively routine charge — rose nearly a quarter. That was part of a 15 % increment in all federal gun prosecutions in the first nine months of 2017.
Three out of every four federal gun charges filed in the 12 months starting in October 2016 were under a statute forbidding felons from owning or transporting a gun, according to Syracuse University’s TRAC database, which monitors gun crime statistics. The period encompasses both the end of the Obama administration and the first several months of Mr. Sessions’s term.
Three law enforcement officials described a newfound interest among prosecutors in taking on smaller gun cases — referred to in law enforcement parlance as one-man, one-gun cases for their narrow shock. Such cases had long been left to state and local prosecutors, freeing Justice Department officials to focus on broader investigations of interstate gun trafficking and criminal networks.
On Jan. 1, 2017, police in York, Pa., stopped Steven Gray, 46, whom they said was carrying a pistol. Mr. Gray was charged in federal court last April with illegally possessing the firearm, which he denied was his. A forensic investigation by the Bureau of Alcohol, Tobacco, Firearms and Explosives found no discernible DNA on the weapon. Mr. Gray, who had a prior felony drug charge, was convicted and faces up to 10 years in prison when he is sentenced in the arriving months.
“Sometimes it appears they’re just looking for numbers,” his lawyer, Thomas Thornton, said of federal prosecutors, who denied the accusation.
“Our efforts are not about numbers,” said David Freed, the United States attorney for the Middle District of Pennsylvania. “We are focused on reducing violent crime and protecting law-abiding citizens.”
But few law enforcement officials want to make a priority of prosecuting low-level offenders, one said, describing simmering concern that the pressure from Mr. Sessions will lead prosecutors to prioritize conviction totals over their impact on crime.
When Mr. Tiemann sought leniency for his client, prosecutors pointed to Mr. Sessions’s policy, he said, telling him that they were “now required to pursue the most serious charge and the most serious punishment available.” Prosecutors initially sought to charge Mr. Amos with an offense that carried a sentence of up to 15 years before settling on a lesser charge, Mr. Tiemann said.
Richard W. Moore, the United States attorney for the Southern District of Alabama, which prosecuted the case, said Mr. Amos’s conviction record “speaks for itself.”
“Consistent with Department of Justice policy, we charge and pursue the most serious, readily provable offense,” said Mr. Moore.
Supporters of Mr. Sessions’s initiatives acknowledge the politics of his approach and remain wary it could be used to sap energy from further legislative or regulatory efforts to combat gun violence, like regulating assault weapons or increasing background check requirements.
“We certainly are hoping for some additional legislative fixes by Congress,” Mr. Manger said.
It is difficult to judge the impact of Mr. Sessions’s initiatives. Many offenders charged with federal gun laws in 2017 are just now going to trial or being sentenced, and some of the cases could still be moved out of the federal system.
Federal firearm prosecutions have historically ebbed and flowed, often spiking in the years following significant court decisions or large-scale mass shootings. After steadily dropping since 2004, prosecutions started increasing again in 2015, according to the TRAC database.
People convicted of firearms-related crimes make up more than 17 percent of the federal prison population, the second-biggest group after drug offenses, Justice Department data showed. Ninety-six percent of defendants convicted of a federal firearms offense in 2017 were sentenced to prison.
“Enforcement isn’t always the solution to those different types of crimes,” said Inimai Chettier, director of the justice program at New York University’s Brennan Center for Justice. “The result might be to increase the federal prison population without a correlating reduction in crime.”
Amid surging public pressure following the mass shooting at a Florida high school in February, Mr. Trump directed Mr. Sessions to more strictly enforce existing gun laws. Survivors of that shooting have pushed Mr. Trump to ban assault weapons and raise the legal purchasing age for firearms.
Instead, prodded by Mr. Trump, Mr. Sessions pushed federal prosecutors to more strictly enforce background check violations and ban bump stocks, a device that can assist semiautomatic weapons fire like machine guns. Bump stocks were used in the Las Vegas massacre in October.
Mr. Sessions explained his rationale at a speech following the Florida shooting.
“It’s not good,” he said, “if we’ve got gun laws that say criminals can’t carry guns and they never get enforced.”