Mangione, 26, has been charged with murdering Thompson in New York City and is expected to plead not guilty. Authorities said they found a three-page handwritten document on Mangione that detailed disdain for the U.S. healthcare system.

A Reddit account under the name mister_cactus has also been located, and it is linked to Mangione’s personal website, offering personal details that match Mangione’s. Reddit did not confirm whether the now-deactivated account belonged to him, but outlets such as the Washington Post viewed the posts through an internet archive, and the details between the user and Mangione matched up.

On Reddit in April, Mangione posted advice about how to get a doctor to perform spinal surgery, but not without a tone of skepticism for the healthcare industry.

“Tell them you are ‘unable to work’ / do your job,” the user wrote. “We live in a capitalist society. I’ve found that the medical industry responds to these key words far more urgently than you describing unbearable pain and how it’s impacting your quality of life.”

The Reddit posts reviewed did not show any signs of aggression toward UnitedHealthcare or other insurers but rather documentation of the user’s struggle with debilitating back pain.

“From childhood until age 23, my back would always ache if I stood too long, but it wasn’t too bad,” the user wrote in February.

As Mangione grew older, his life became more disrupted. Cognitive problems, as well as chronic back pain, became the norm by his mid-20s.

“The people around you probably won’t understand your symptoms – they certainly don’t for me,” mister_cactus wrote in a Reddit group for brain fog.

Mangione was reportedly living at Surfbreak HNL, a co-living community in Honolulu, in January 2022 when a surfing accident worsened his spinal condition, according to his Reddit posts. In July 2023, he had a spinal fusion surgery, a procedure that stabilizes the spine with surgical screws.

According to the Reddit posts, Mangione seemed happy with the results, writing, “Haven’t had a bad day since,” in November 2023.

Mangione had posted a picture of his spinal X-ray on his X account, showing a direct connection to the surgery explained in the Reddit posts. The outlet asked an orthopedic surgeon to review the X-ray, with the doctor describing it as a “lumbar spine with posterior spinal instrumentation, possible fusion.”

The procedure is common for people diagnosed with spondylolisthesis, a condition where spinal vertebrae slip forward out of place, causing excruciating pain in the lower back.

Authorities have not said how they believe Mangione escalated from frustration with the U.S. healthcare system into premeditated murder.

Mangione was denied bail and is currently contesting extradition to New York, leaving Pennsylvania with 30 days to get a warrant from Gov. Kathy Hochul (D-NY) for extradition.