Authorities believe Kaitlin Armstrong -- the woman accused of killing a professional cyclist in Texas last year -- may have been preparing for months before she tried to escape custody during a doctor's appointment last week, court documents show.

An investigation of her attempted escape revealed Armstrong had been "exercising vigorously" for months before she broke free from corrections officers while being escorted from a medical appointment last Wednesday, leading them on a foot chase for about a mile before she was recaptured, according to an affidavit.

She had also complained of an injury that would mean she could get the medical appointment outside her jail and secured a medical request that would prevent her legs from being restrained, the affidavit said.

Armstrong has been in custody since she was captured in Costa Rica in June last year and deported to the US to face a first-degree murder charge in the fatal shooting of Anna Moriah "Mo" Wilson at an Austin home in May 2022, to which she has pleaded not guilty, authorities said.

She is now facing an additional felony charge of escape causing bodily injury, according to the affidavit, which was filed on Friday in support of the charge.

CNN has reached out to Armstrong's attorney for comment on the new charge.

How authorities say Armstrong briefly broke free

Armstrong tried to make her escape as two corrections officers were leading her out of the back door of a medical office after her appointment last Wednesday, according to the affidavit. She was somehow able to break free and run away as the officers followed her, the document said.

As she ran, Armstrong removed her black and white striped jail uniform pants to reveal she had put on thermal pants underneath "in an effort to disguise her appearance as an inmate," the document said.

Armstrong was also able to free one of her hands from her restraints, according to the document. During a later search of her cell, investigators found a broken, thin piece of metal that could likely be used to remove a handcuff, it said.

During the pursuit, Armstrong tried to scale a six-foot fence before an officer pulled her down, causing both of them to fall, the affidavit said. But Armstrong immediately got back up and kept running, according to the document.

Video taken by a witness shows a person, who appears to be Armstrong, running along a small hill next to a fenced-in parking lot as she is pursued by an officer. The person then pulls herself to the top of a fence, which is several feet tall. Behind her, the officer trips and falls before getting back up. The video stops just as the person being pursued pulls her torso to the top of the fence.

Armstrong ran for about a mile, ignoring officers' commands to stop and the sound of sirens from several responding law enforcement units, the affidavit said.

Video footage from the detention facility where Armstrong is being held showed she had been "exercising vigorously" for months, including running, doing squats and practicing yoga, according to the document.

Both corrections officers suffered injuries to their arms and knees during the pursuit, the affidavit notes, though further details on the nature of the injuries were not provided.

After Armstrong was caught, she was taken to a local hospital and then returned to sheriff's office custody, the agency said last week.

A jury trial on the charges Armstrong faces related to Wilson's killing is scheduled for October 30, according to court records.