Officer J.R. Smith told a state judge Thursday that he regretted what had happened.
"I'm sorry," the 35-year-old said, his voice barely audible. He pleaded guilty to manslaughter, violation of oath, criminal solicitation, making false statements and perjury, which was based on claims in a warrant.
Former Officer Gregg Junnier, 40, who retired from the Atlanta police in January, pleaded guilty to manslaughter, violation of oath, criminal solicitation and making false statements. Both men are expected to face more than 10 years in prison.
In a hearing later in federal court, both pleaded guilty to a single charge of conspiracy to violate a person's civil rights, resulting in death. Their state and federal sentences would run concurrently.
The charges followed a Nov. 21 "no-knock" drug raid on the home of Kathryn Johnston, 92. An informant had described buying drugs from a dealer there, police said. When the officers burst in without warning, Johnston fired at them, and they fired back, killing her.
Fulton County prosecutor Peter Johnson said that the officers involved in Johnston's death fired 39 shots, striking her five or six times, including a fatal blow to the chest.
He said Johnston fired only once through her door and didn't hit any of the officers. That means the officers who were wounded likely were hit by their own colleagues, he said.
Junnier and Smith, who is on administrative leave, had been charged in an indictment unsealed earlier Thursday with felony murder, violation of oath by a public officer, criminal solicitation, burglary, aggravated assault with a deadly weapon, and making false statements.
The third officer, Arthur Tesler, also on administrative leave, was charged with violation of oath by a public officer, making false statements and false imprisonment under color of legal process. His attorney, William McKenney, said Tesler expects to go to trial.
Both men could have faced up to life in prison had they been convicted of murder. Instead, Junnier will face 10 years and one month and Smith 12 years and seven months. No sentencing date was immediately set, and the sentences are contingent on the men cooperating with the government.
The deadly drug raid had been set up after narcotics officers said an informant had claimed there was cocaine in the home.
When the plainclothes officers burst in without notice, police said, Johnston fired at them, and they fired back.
Assistant U.S. Attorney Yonette Sam-Buchanan said Thursday that although the officers found no drugs in Johnston's home, Smith planted three bags of marijuana in the home as part of a cover story.
The case raised serious questions about no-knock warrants and whether the officers followed proper procedures.
Atlanta Police Chief Richard Pennington asked the FBI to lead a multi-agency probe. He also announced policy changes to require the department to drug-test its nearly 1,800 officers and require top supervisors to sign off on narcotics operations and no-knock warrants.
To get the warrant, officers told a magistrate judge that an undercover informant had told them Johnston's home had surveillance cameras monitored carefully by a drug dealer named Sam.
After the shooting, a man claiming to be the informant told a television station that he had never purchased drugs there, leading Pennington to admit he was uncertain whether the suspected drug dealer actually existed.
The Rev. Markel Hutchins, a civil rights activist who serves as a spokesman for Johnston's family, said the family was satisfied with Thursday's developments.
"They have never sought vengeance. They have only sought justice," he said.
Hutchins said the family is considering civil action against the police department.
"I think what happened today makes it very clear that Ms. Johnston was violated, that her civil rights were violated," he said.