The death of an Alabama jail official who shot herself rather than surrender to US Marshals has only deepened the mystery of why a trusted manager would help free a hulking murder suspect with a violent and frightening history.

Vicky White, 56, was pronounced dead in hospital after Casey White, 38, gave up without a fight in Evansville, Indiana. They had spent more than a week on the run through three states.

NBC’s Today show reported that federal marshals said Casey White told officers at the scene: “Please help my wife. She just shot herself in the head and I didn’t do it.”

Before Vanderburgh County coroner Steve Lockyear announced her death, the sheriff in Alabama had said he hoped to get answers from his once trusted jail employee.

“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,” Lauderdale County Sheriff Rick Singleton said.

Authorities closed in after receiving a tip on Sunday that a man resembling Casey White had been recorded by a surveillance camera at a car wash getting out of a 2006 Ford F-150 pickup truck, the Marshals Service said. White is 6ft 9in tall and weighs more than 18st.

A local police officer then spotted a vehicle they were looking for on Monday, and members of a US Marshals taskforce went to investigate, leading to a brief chase, Vanderburgh County Sheriff Dave Wedding said.

He added: “The pursuit was very short. It went up a major artery here in Vanderburgh County and they cut across a parking lot at a large factory. They were in a grassy area so three of our taskforce members actually rammed the vehicle, pushed it into a ditch so it ended up on its side.

“As they approached the vehicle it was obvious that the female driver was unconscious and still had a weapon in her hand. And they removed the murderer from the vehicle simultaneously.

“The coroner’s office will do an investigation and they will determine if it was a self-inflicted gunshot wound. The initial indication is that it was, but we won’t rule anything out until we have a thorough investigation by the coroner.”

The manhunt began on April 29 after Vicky White, the assistant director of corrections for the jail in Lauderdale County, told co-workers she was taking Casey White, who was awaiting trial in a capital murder case, from the jail for a mental health evaluation.

The two, who are not related, fled the area.

Mr Singleton said: “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.”

Casey White was serving a 75-year sentence for attempted murder and other charges at the time of his escape. He was awaiting trial for 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 also learned that 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 White charging her with permitting or facilitating escape in the first degree. Her family and co-workers said they were stunned.

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 recent months, she had bought a rifle and a shotgun and also was known to have a handgun, US Marshal Marty Keely said.

She also sold her house — for about half of market value — and bought a 2007 Ford Edge that she parked 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.

Vicky White said it would be her last day at work. No mental health evaluation was scheduled, and 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.