The authorities in Alabama said on Monday that they had issued an arrest warrant for a corrections officer who disappeared with a murder suspect after they left a jail together last week for an appointment that turned out not to exist.

The officer, Vicki White, the assistant director of corrections for Lauderdale County, Ala., left the county jail at 9:41 a.m. on Saturday to take the inmate, Casey White, to a mental health evaluation at the county courthouse in Florence, just outside Muscle Shoals. Though Officer White and Mr. White have the same surname, they are not related, officials said.

The Lauderdale County sheriff, Rick Singleton, said at a news conference on Monday that an arrest warrant had been issued for Officer White on a charge of permitting or facilitating an escape in the first degree.

But, Sheriff Singleton said, it was not yet clear if Officer White, who disappeared the day she was to retire from the sheriff’s office, had been coerced or threatened. “We know for sure she did participate,” he said.

Mr. White, who was charged with two counts of capital murder in 2020 in connection with a murder for hire, should have had two deputies with him at all times, the sheriff said. That includes during transportation to the courthouse, which was a three-minute drive away. The sheriff said that Officer White violated policy by transporting him alone.

Sheriff Singleton said she had told the booking officer that she would drop Mr. White off at the courthouse herself to catch up with two vans carrying inmates that had just left.

She also told the booking officer that she would “seek medical assistance” for herself after dropping off Mr. White for his appointment because she was feeling ill. But Officer White did not go to a medical appointment, either, Sheriff Singleton said.

“We think that was an excuse,” he said.

Instead, they disappeared, prompting a search.

The authorities said they began to investigate whether there had ever been a relationship between the two and whether Officer White had helped Mr. White escape, a possibility that seemed out of character for one of the most respected and senior figures at the jail.

“This is not the Vicki White we know,” Sheriff Singleton said.

The sheriff said that Officer White had spoken about her retirement before she suddenly disappeared with Mr. White. She had talked about going to the beach and had recently sold her house, he said.

“Everybody thought she was going to retire,” Sheriff Singleton said. “Nobody saw this coming.”

The authorities continued their search on Monday. Officer White’s abandoned patrol car was found on Friday morning, parked among cars for sale at Florence Square, a shopping mall two miles from the jail. Investigators determined that they had not gone to the courthouse at all, the sheriff said.

He said investigators were scrutinizing surveillance video footage and call records to determine whether the two had “any kind of relationship.”

Officer White’s duties included scheduling transportation for inmates to appear in court and arranging for them to be escorted by armed deputies. The possibility that she had facilitated an inmate’s escape stunned her fellow employees, the sheriff said. In Sheriff Singleton’s seven years in the position, Officer White had been voted the department’s employee of the year four times, he said last week. She had been chosen from more than 50 people working at the jail, he said.

Mr. White is 6-foot-9 and weighs between 250 and 275 pounds. He was handcuffed and shackled when he left the jail, Sheriff Singleton said. The U.S. Marshals Service said on Sunday that it was offering a $10,000 reward for information leading to the capture of Mr. White and the location of Officer White.

The Alabama Law Enforcement Agency issued a “blue alert” on Friday night for the missing officer. “Casey White is believed to be a serious threat to the corrections officer and the public,” the alert said.

Sheriff Singleton said Officer White was armed with a 9-millimeter handgun before she disappeared, leading investigators to believe that Mr. White was now armed.

Isabella Grullón Paz and Alex Traub contributed reporting.