The scion of a prominent Maryland family who came top of his class at an elite private school before graduating from an Ivy League college, Luigi Mangione seemed to have everything going for him, according to friends.

They have been left stunned by the 26-year-old's arrest for the murder of UnitedHealthcare's chief executive Brian Thompson, who was fatally shot last week in New York City. Mr Mangione will plead not guilty, his lawyer says.

According to a law enforcement bulletin seen by US media, Mr Mangione was allegedly motivated by resentment at what he called "parasitic" health insurance companies.

He had spent time in a surfing community in Hawaii, but left owing to debilitating back pain, say those who remember him. It is unclear, however, to what extent his own health troubles shaped his views of the medical industry.

He was arrested on Monday at a McDonald's in Altoona, Pennsylvania, and was allegedly in possession of a gun, bullets, multiple fake IDs and cash.

Mr Mangione also had a handwritten document that expressed "ill will" towards corporate America and included passages such as "frankly, these parasites had it coming", according to police.

Investigators say the words "deny", "defend" and "depose" were written on shell casings found at the scene of Mr Thompson's murder.

Law enforcement sources say this may be a reference to the "three Ds of insurance" - tactics used by companies to reject payment claims by patients.

Mr Mangione comes from a prominent family in the Baltimore area who are known for businesses including country clubs, nursing homes and a radio station according to local media.

The suspect's paternal grandparents, Nicholas and Mary Mangione, were real estate developers who purchased the Turf Valley Country Club in 1978 and Hayfields Country Club in Hunt Valley in 1986.

Shortly after Mr Mangione was charged, his cousin, Republican state lawmaker Nino Mangione, released a statement saying the family was "shocked and devastated".

"We offer our prayers to the family of Brian Thompson and we ask people to pray for all involved", the statement read.

Thomas Maronick, a defence attorney who knows members of the family, told the BBC of his shock at the charges.

"You wouldn't think someone of privilege or means from a family that's known for doing so much for the community would do something like this," he said.

Mr Mangione attended the private, all-boys Gilman School in Baltimore. He was valedictorian, an accolade usually bestowed on the student with the highest academic achievements.

Speaking to the BBC's US partner, CBS News, one of his classmates said Mr Mangione "didn't have any enemies" and was a "valedictorian for a reason".

Mr Mangione went on to graduate from the University of Pennsylvania, where he gained a bachelor's and master's degree in computer science, according to the school, and founded a video game development club.

A friend who attended the Ivy League college at the same time as Mr Mangione described him as a "super normal" and "smart person".

Mr Mangione was employed as a data engineer for TrueCar, a digital retailing website for new and used cars, according to his social media profiles. A company spokesman told the BBC he had not worked there since 2023.

He also spent time in a co-living surfing community in Hawaii called Surfbreak. Sarah Nehemiah, who knew him then, told CBS he left due to his back injury, which had worsened from surfing and hiking.

Friends have told US media he had surgery on his back. The background image on an X account believed to belong to Mr Mangione shows an x-ray of a spine with hardware in it.

On a Reddit account that appears to have belonged to him, Mr Mangione reportedly posted about his struggles with chronic back pain and brain fog.

A former roommate, RJ Martin, told the BBC that while Mr Mangione "never complained", his back pain at times "prohibited him" from doing "many normal things", such as surfing or playing volleyball.

Mr Martin - who eventually lost contact with Mr Mangione - said that he believed his former friend "would have never conceived of hurting someone else".

"There's no making sense of it," he added.

A person matching his name and photo had an account on Goodreads, a user-generated book review site, where he read two books about back pain in 2022, one of them called Crooked: Outwitting the Back Pain Industry.

He also gave four stars to a text called Industrial Society and Its Future by Theodore Kaczynski – also known as the Unabomber manifesto.

Starting in 1978, Kaczynski carried out a bombing campaign that killed three people and injured dozens of others, until he was arrested in 1996.

In his review, Mr Mangione acknowledged Kaczynski was a violent individual, but also described him as a political revolutionary.

According to local media reports, Mr Mangione's mother had reported him missing last month to San Francisco authorities, telling them she had not heard from her son since July.