A former Alabama jail official has died and the murder suspect she is accused of helping escape from custody has been apprehended in Indiana after more than a week on the run.

The death of Vicky White, 56, only deepened the mystery of why a respected jail official would leave everything to help free Casey White, 38, a hulking inmate with a violent and frightening history.

The two fugitives were caught - following a manhunt through three states - in Evansville, Indiana, when US Marshals chasing them crashed into their vehicle, authorities said.

Casey White gave himself up and Vicky White shot herself and was taken to a hospital. Vanderburgh County Coroner Steve Lockyear said she died from her injuries.

Before Vicky White's death, authorities celebrated the fugitives' apprehension.

"We got a dangerous man off the street today. He is never going to see the light of day again. That is a good thing, for not just our community. That's a good thing for our country," Lauderdale County Sheriff Rick Singleton of Alabama said.

The manhunt began on April 29 when Vicky White, the assistant director of corrections for the jail in Lauderdale County, allegedly helped engineer the escape of Casey White, who was awaiting trial in a capital murder case.

Vicky White had told co-workers she was taking the inmate from the jail for a mental health evaluation at the courthouse, but the two, who are not related, instead fled the area.

The car they took off in was later found abandoned in Tennessee, but there was no trace of the pair until US Marshals received a tip on Sunday that surveillance photos from an Evansville car wash showed a man who closely resembled Casey White exiting a 2006 Ford F-150 pickup truck, the Marshals Service said. White stands 6 feet, 9 inches (2.06 metres) tall and weighs about 260 pounds (118 kilograms).

On Monday, officials learned that the pair was spotted near the sheriff's office, said Vanderburgh County Sheriff Dave Wedding in Indiana.

As officers arrived, the pair fled in a vehicle and led police on a pursuit before US Marshals collided with them "to try to end the pursuit", he said.

Mr Wedding added Casey White was injured, not too seriously, in the crash and Vicky White then shot herself, causing "very serious" injuries.

"We're lucky that no law enforcement was injured, no innocent civilians were injured, the pursuit was short in nature and we have both people in custody," he said.

Casey White was serving a 75-year prison sentence for attempted murder and other charges at the time of his escape. He was awaiting trial in the stabbing of a 58-year-old woman during a burglary in 2015. If convicted, he could face the death penalty.

Federal and local law enforcement officials have also learned Casey White threatened to kill his former girlfriend and his sister in 2015 and said "that he wanted police to kill him", the Marshals Service said.

A warrant was issued on May 2 for Vicky Sue White charging her with permitting or facilitating escape in the first degree.

Before her death was announced, the Alabama sheriff said he hoped to get answers from his once trusted jail employee about her actions but acknowledged those answers might not come.

"I had every bit of trust in Vicky White. She has been an exemplary employee. What in the world provoked her, prompted her to pull a stunt like this? I don't know. I don't know if we'll ever know," Mr Singleton said.

Vicky White's family members and co-workers said they were stunned by her involvement. Mr Singleton said it appeared the plan had been in the works for some time. Jail inmates said the two had a special relationship and she gave Casey White better treatment than other inmates.

In the past several months, she bought a rifle and a shotgun and also was known to have a handgun, US Marshal Marty Keely said.

She sold her house for about half of market value and bought a 2007 orange Ford Edge that she stashed at a shopping centre without licence plates.

"This escape was obviously well-planned and calculated. A lot of preparation went into this. They had plenty of resources, had cash, had vehicles," Mr Singleton said.

The escape happened on what Vicky White said was going to be her last day at work. She told co-workers that Casey White had a mental health evaluation at the courthouse, but none was scheduled. She did not have a second officer accompany them, which was against jail policy.

Video showed the pair went from the jail to the shopping centre, where they picked up the Ford and left, Mr Singleton said. Their flight was not discovered for much of the day.