Who is Luigi Mangione? Ex-roommate details relationship with Maryland native, healthcare CEO murder suspect

BALTIMORE -- A banner over the Jones Falls Expressway in North Baltimore reads "deny, defend, depose," an indictment of the American healthcare industry, and the same words police say were written on the bullets Maryland native Luigi Mangione allegedly used to kill United Healthcare CEO Brian Thompson.

Thompson was shot and killed on December 4 in New York City.

But what may have caused the wealthy heir to a high-profile Baltimore family to snap?

A handwritten note found on Mangione railed against the healthcare industry and stated, "Frankly, these parasites simply had it coming."

Former roommate speaks

R.J. Martin, who lived with Mangione in Hawaii, said his former roommate recently underwent surgery for crippling back pain. 

Martin said he bonded with Mangione over workouts, volleyball and yoga classes.

"He didn't disclose a lot about it. I knew it was an issue," Martin said. "I knew it inhibited him from doing a lot of activities he wanted to, but when he wasn't in pain, he was extremely active."

Mangione posted an X-ray on social media.

"He was suffering from a spinal misalign that had been ongoing for quite some time and that something had to do with his care back home," Martin said. "So that always was weighing on him, returning home so that he could see his doctor," Martin said. 

Prominent Baltimore family

Mangione's family owns Lorien Health Services, a chain of nursing homes across suburban Baltimore. They also own WCBM radio, a conservative news-talk station where his arrest was the hourly top story on Tuesday. 

The Mangione family also developed Turf Valley, a country club in Howard County, and Hayfields Country Club in Hunt Valley. 

ProPublica estimates their charity arm, the Mangione Family Foundation, is worth more than $4 million.

The aquatic center at Loyola University is named after them. The family also supported the Greater Baltimore Medical Center.

"Surprisingly, I don't recall any deep conversations specifically regarding healthcare," Martin said. "We definitely talked about systems and politics and dysfunction and why people don't solve problems, why good people can't come together and find common ground when perhaps it's obvious." 

The wealth, in part, comes from his grandfather Nicholas Mangione — a self-made multimillionaire. 

His cousin Nino Mangione is a Republican state delegate representing Baltimore County

Gilman valedictorian 

Mangione was the Class of 2016 valedictorian at the elite Gilman School in North Baltimore, which costs close to $40,0000 per year to attend.

In a speech at the time, Mangione addressed parents and said, "Sending us to Gilman was far from a small financial investment."  

Mangione reported missing before arrest

In the months before the killing in Manhattan, Mangione's loved ones became worried. 

Some posted to Twitter, with one saying, "Nobody has heard from you in months." Another wrote, "I don't know if you are ok or just in a super isolated place."

According to a published report, his mother reported him missing to police in San Francisco in November.

"I just feel heartbroken," Martin told CBS News. "Somebody that I loved and cared about that could have done something so hideous, but also that, his life effectively, it's probably forever over and altered and just hurts."

Mangione's family said in a statement Monday they are "shocked and devastated." 

Martin also has this message for his friend: "Just tell him that there's a lot of people that really love him and care about him," he said. "And it doesn't undo what he did. He's going have to be responsible for his actions, but he has a community and a deep community of people that really respect him, and in the long term he has friends and I'm sure family that will be there for him."