Who is Luigi Mangione? Loved ones describe alleged Brian ...

For alleged killer Luigi Mangione's friends and family, seeing him in an orange jumpsuit before a courtroom would be a stark contrast to their memories.

Mr Mangione, 26, is accused of fatally shooting UnitedHealthcare CEO Brian Thompson on the footpath outside a hotel last Wednesday morning, local time.

He has been denied bail and will face extradition from Pennsylvania on a murder charge.

Labelled a "thoughtful" and "unassuming" man by those who knew him, they are now left to confront a brutal alleged crime.

A valedictorian at an elite prep school

Mr Mangione grew up the grandson of eminent Maryland real estate developer Nick Mangione.

His childhood involved a country club and an education from one of Baltimore's most elite prep schools, The Gilman School.

Thomas Maronick, a defence attorney who knew the family, described the Mangiones to the BBC as "one of the best-known families" in Baltimore County.

The family owns a golf course and local radio station and is "known for being some of the greatest charitable contributors" to Italian-American causes, he said.

Mr Mangione would go on to become school valedictorian in 2016.

Former classmate Freddie Leatherbury told CNN that Mr Mangione "had everything going for him".

"He was humble," Mr Leatherbury said.

"He was unassuming and easy to approach."

The Maryland native then earned undergraduate and graduate degrees in computer science in 2020 from the University of Pennsylvania.

Luigi Mangione posted this photo at Stanford University in 2019 on his Facebook account. (Supplied: Facebook)

Since the charges, Mr Mangione's family has made a statement detailing their shock — courtesy of his politician cousin Nino Mangione.

"We offer our prayers to the family of Brian Thompson and we ask people to pray for all involved," he posted to social media platform X.

However, it would be a trip to Hawaii that revealed more than just an affluent and educated image.

'I loved this guy'

In 2022, Mr Mangione spent several months in a co-living space called Surfbreak in Waikiki, Hawaii.

Pictures of his time there show him smiling, sometimes shirtless, enjoying the beach and partying.

The space's founder, RJ Martin, was stunned by the arrest, telling local publication Civil Beat: "I loved this guy."

Mr Mangione returned to Hawaii in 2023 for a brief period of time. (AP: Hawaii Dept. of Land and Natural Resources)

"I can make zero sense of it," he later told CNN.

Jackie Wexler also used to live with Mr Mangione at Surfbreak.

"He was just such a thoughtful and deeply compassionate person at everything he did," she told Civil Beat.

But friends also describe a life of chronic pain behind the smiles.

Luigi Mangione's apparent history of back pain

Reuters has not been able to determine whether Mr Mangione had been diagnosed with a back condition.

However, he left a trail of clues on social media, including a picture of an X-ray of a spinal surgery on his X profile and a review on Goodreads of a book called Crooked: Outwitting the Back Pain Industry and Getting on the Road to Recovery.

In a several-page document that Sky News identified as having been uploaded to Mr Mangione's Google Drive account in 2021, the accused gunman said he had a back injury known as an L5-S1 isthmic spondylolisthesis.

The condition means one of the bones in the spine slips forward and presses on the vertebra below it.

Mr Mangione in 2019. (Facebook: Luigi Mangione)

ABC was not able to independently verify this document.

A colleague at his previous employer, Truecar, said Mr Mangione took leave during the middle of 2023 for about two months due to back-related issues.

He said that the company offered employees health insurance through UnitedHealth as well as other choices, including Aetna.

A spokesman for Surfbreak also said Mr Mangione told Mr Martin he had severe back pain that impacted everything from surfing to dating.

"He knew that dating and being physically intimate with his back condition wasn't possible," Mr Martin told the New York Times.

"I remember him telling me that, and my heart just breaks."

Paul Piek, a 21-year-old German who met Mr Mangione in March in Thailand, said the 26-year-old said he did muay Thai before his injury.

A book club suggestion too seems to further spur Mr Mangione's pain into ideology.

People gather outside Blair County Court House, where Mr Mangione made his first court appearance. (Reuters: Eduardo Munoz)

'Fascinated' by Unabomber's ideology

Back in Hawaii, Ms Wexler and Mr Martin told Civil Beat they suggested the manifesto of Ted Kaczynski, better known as the Unabomber, as "a joke" for Surfbreak's book club.

A Goodreads poster with Mr Mangione's name later labelled Kaczynski's book, Industrial Society and Its Future, "prescient" about modern society.

He also deemed him an "extreme political revolutionary" and suggested violence was a legitimate form of resistance in some circumstances.

Unabomber Ted Kaczynski was sentenced to four life sentences. (AP: John Youngbear)

While the ABC cannot confirm the account's link to Mr Mangione, an English writer would appear to verify the interest.

Gurwinder Bhogal told The New York Times he struck up a relationship with Mr Mangione while the latter was living in Japan.

Bhogal said he was bewildered by the charges, calling Mr Mangione "thoughtful and soft-spoken".

The pair reportedly had a lengthy email exchange and in one instance, Kaczynski once again became a topic of discussion.

"Luigi disapproved of the Unabomber's actions," Mr Bhogal told the US publication via email.

"But was fascinated by his ideology, and shared his concerns about rampant consumerism gradually eroding our agency and alienating us from ourselves."

Then, the emails stop.

Police believe Mr Mangione's alleged murder of Brian Thompson was "premeditated". (Supplied: NYPD via X)

Mr Mangione disappears for months

Despite his global ties, most agree communication with Mr Mangione falls "radio silent" come June or July of this year.

The New York Times reported his mother also filed a missing person report for her son on November 18.

From there, the public can only use Mr Mangione's social media posts to gather a final portrait of the man who would go on to be charged with murder.

Some posts are notably health-conscious — posts imploring the dangers of smartphones for children, or exercise habits.

Police will allege Mr Mangione shot Mr Thompson outside a New York hotel. (Reuters/NYPD News)

Others grow more sinister in light of his arrest.

A quote from Indian philosopher Jiddu Krishnamurti exhorts the perils of becoming "well-adjusted to a profoundly sick society".

Police will allege it is this mindset that led to a final manifesto and the murder of Mr Thompson.

And until Mr Mangione speaks out, the trail may be the clearest indication of his thoughts prior to his alleged assassination.

"I do apologize for any strife or traumas but it had to be done," Mr Mangione allegedly writes in his three-page document.

"Frankly, these parasites simply had it coming."

ABC/Wires