Luigi Nicholas Mangione wrote that the United States has the most expensive health care system in the world and that profits of major corporations continue to rise while "our life expectancy" does not, according to the bulletin, based on a review of his hand-written notes and social media posts.
Prosecutors on Tuesday were beginning to take steps to bring Mangione back to New York to face a murder charge while new details emerged about his life and how he was captured.
The 26-year-old Ivy League graduate from a prominent Maryland real estate family was expected to be in court a day after police arrested him in a Pennsylvania McDonald's.
He was charged with murder hours after he was arrested on Monday in the killing of Brian Thompson, who led the country's largest medical insurance company.
Mangione remained jailed in Pennsylvania, where he was initially charged with possession of an unlicensed firearm, forgery and providing false identification to police.
Manhattan prosecutors have obtained an arrest warrant, a step that could help expedite his extradition from Pennsylvania.
Court officials have said that Mangione does not yet have a lawyer who can comment on the allegations.
Asked at Monday's arraignment whether he needed a public defender, Mangione asked whether he could "answer that at a future date".
Mangione called "Unabomber" Ted Kaczynski a "political revolutionary" and may have found inspiration from the man who carried out a series of bombings while railing against modern society and technology, according to the police bulletin.
Mangione was arrested in Altoona, Pennsylvania - about 370km west of New York City - after a McDonald's customer recognised him and notified an employee, authorities said.
Officers found him sitting at a back table, wearing a blue medical mask and looking at a laptop, according to a Pennsylvania police criminal complaint.
He initially gave them a fake ID but when an officer asked Mangione whether he had been to New York recently, he "became quiet and started to shake," the complaint says.
When he pulled his mask down at officers' request, "we knew that was our guy," rookie Officer Tyler Frye said.
Images of Mangione released on Tuesday by Pennsylvania State Police showed him pulling down his mask in the corner of the McDonald's while holding what appeared to be hash browns and wearing a winter jacket and beanie.
In another photo from a holding cell, he stood unsmiling with rumpled hair.
New York Police Commissioner Jessica Tisch said Mangione was carrying a gun like the one used to kill Thompson and the same fake ID the shooter had used to check into a New York hostel, along with a passport and other fraudulent IDs.
NYPD chief of detectives Joseph Kenny said Mangione also had a three-page, handwritten document that shows "some ill will toward corporate America".
A law enforcement official who was not authorized to discuss the investigation publicly and spoke with The Associated Press on condition of anonymity said the document included a line in which Mangione claimed to have acted alone.
"To the Feds, I'll keep this short, because I do respect what you do for our country. To save you a lengthy investigation, I state plainly that I wasn't working with anyone," the document said, according to the official.
It also had a line that said, "I do apologise for any strife or traumas but it had to be done. Frankly, these parasites simply had it coming".
A grandson of a wealthy, self-made real estate developer and philanthropist, Mangione is a cousin of a current Maryland state legislator.
Valedictorian at his elite Baltimore prep school, he went on to earn undergraduate and graduate degrees in computer science in 2020 from the University of Pennsylvania, a spokesperson said.
"Our family is shocked and devastated by Luigi's arrest," Mangione's family said in a statement posted on social media late on Monday by his cousin Maryland state delegate Nino Mangione.
"We offer our prayers to the family of Brian Thompson and we ask people to pray for all involved."
