A federal judge on Wednesday sentenced a man convicted in the 2010 killing of a United States Border Patrol agent to life in prison, closing another chapter in a case that revealed the botched gun-smuggling investigation known as Operation Fast and Furious.

Judge David C. Bury of United States District Court in Arizona sentenced the man, Heraclio Osorio-Arellanes, to a life term in the killing of the agent, Brian A. Terry, who was fatally shot during a firefight with an armed crew who was attempting to rob drug smugglers in rural Arizona on Dec. 14, 2010.

Last year, a federal jury found that Mr. Osorio-Arellanes, 41, was part of the armed crew of bandits who murdered Agent Terry and convicted him of nine counts, including first-degree murder.

The killing of Agent Terry became the emotional centerpiece of a politically charged confrontation between congressional Republicans and the Obama administration over the wisdom and execution of Operation Fast and Furious.

The operation was conducted from late 2009 to early 2011 by Phoenix-based agents of the Bureau of Alcohol, Tobacco, Firearms and Explosives who were looking into a gun-smuggling network linked to a Mexican drug cartel.

Suspected “straw” purchasers for the network acquired about 2,000 guns, most of which were presumed to have reached drug gangs. In December 2010, two weapons that had been bought by one of the suspects were found at the site of the shootout in which Agent Terry was killed, setting off a scandal.

Mr. Osorio-Arellanes, who was taken into custody by Mexican authorities in 2017, was the sixth of seven defendants convicted and sentenced in the case. Prosecutors said that Jesus Favela-Astorga, the sole defendant still facing trial, was also arrested by Mexican authorities in 2017 and was awaiting extradition to the United States.

Agent Terry’s sister Michelle Balogh said Wednesday that she had traveled from her home in Michigan to witness the sentencing of Mr. Osorio-Arellanes in Tucson, along with another sister, Kelly Willis. Ms. Balogh, 51, said she had not missed a single hearing in the criminal cases stemming from the killing of her brother, and was satisfied that Mr. Osorio-Arellanes was sentenced to life in prison.

“It’s only fair,” Ms. Balogh said. “Brian doesn’t get to walk among us, so why should he?”

Mr. Osorio-Arellanes’s lawyer did not respond to messages seeking comment on Wednesday.

Robert Brewer, the United States attorney for the Southern District of California, said the sentence could not eliminate the suffering of Agent Terry’s family, but he hoped it would bring them “some degree of comfort.”

“Brian Terry exemplified the very best of law enforcement: A selfless, determined agent who was committed to protecting the people of the United States,” Mr. Brewer said in a statement.

In 2012, the Justice Department’s inspector general issued a scathing critique of federal officials for their handling of Operation Fast and Furious. The report faulted Arizona-based prosecutors and bureau agents for “a series of misguided strategies, tactics, errors in judgment and management failures” that allowed the risky operation to continue despite the danger to public safety.

That year, the Republican-led House voted to hold Attorney General Eric H. Holder Jr. in contempt of Congress because the Justice Department did not turn over documents related to the case. President Barack Obama asserted executive privilege to block a congressional subpoena.

Some Republicans and commentators on conservative news media outlets floated theories that senior Obama officials must have approved the operation — deliberately fostering gun violence to provide a rationale for strengthening gun-control laws — and that they were engaged in a cover-up.

Ms. Balogh said Wednesday that she was frustrated that officials involved in the operation were not criminally charged.

“I wish we could get the truth on that, and hold those accountable who were part of that program, so they could go to prison, as well,” she said.

Credit…U.S. Customs and Border Protection , via Associated Press