A man arrested in connection with the shooting of an insurance executive in New York was carrying a handwritten document suggesting he had "ill will towards corporate America", US police say.
Luigi Mangione, 26, has been charged with weapons and other offences after he was arrested at a Pennsylvania McDonald's. A customer recognised his face from media coverage and notified an employee, who called police, officers said.
They said Mr Mangione initially produced a fake ID when approached by officers at the McDonald's.
When they asked him to remove his face mask, they recognised him as a suspect in the killing and asked if he had been in New York City recently.
"That really invoked a physical reaction from the suspect," local police Deputy Chief Derek Swope said. "He became visibly nervous, kind of shaking, at that question."
He has now been charged with carrying a gun without a licence, forgery, falsely identifying himself to the authorities and possessing instruments of crime.
He was denied bail and remains in custody in Pennsylvania. He is expected to be charged with more offences after being extradited to New York.
New York police earlier said Mr Mangione was found with a "ghost gun", possibly produced by a 3D printer, and a silencer similar to that used to kill UnitedHealthcare CEO Brian Thompson on Wednesday.
His mask and clothing were similar to those worn by the suspect in CCTV images released by detectives.
He also had multiple fake IDs, including one that matched that used by the suspect to check into a hostel in Manhattan before the shooting.
And he was carrying a "handwritten document that speaks to his motivation and mindset", New York Police Commissioner Jessica Tisch said.
"We don't think there's any specific threats to other people mentioned in that document," NYPD Chief of Detectives Joseph Kenny told a media conference.
"But it does seem that he has some ill will toward corporate America."
The New York Times, citing an unnamed official, earlier reported he had a handwritten "manifesto" criticising healthcare companies for prioritising profits over care.
Mr Mangione is originally from Maryland but his last known address was in Honolulu, Hawaii, Chief Kenny said.
The 50-year-old victim was shot in the street as he walked to the Hilton hotel in Midtown Manhattan for an investor conference.
It's been widely reported that the bullet casings found at the scene had the words "delay", "deny" and "depose" written on them.
It's been interpreted as a possible reference to "delay, deny, defend", a phrase often used by critics of America's corporate health insurance industry.
The sector has a reputation for underpaying and refusing to pay, claims, and medical debt is now the most common cause of personal bankruptcy in the US.
The UnitedHealth Group and other corporate insurers have taken steps to protect their executives after social media users celebrated the killing and expressed anger at the industry in posts that were sent viral.
Pennsylvania Governor Josh Shapiro said Mr Thompson's killer was wrongly being "hailed as a hero" by some.
"I understand people have frustration with our healthcare system … but I have no tolerance, nor should anyone, for one man using an illegal ghost gun to murder someone because he thinks his opinion matters most."
Last week, the FBI announced it was offering a $US50,000 ($77,000) reward for information leading to an arrest and conviction on top of a $US10,000 reward offered by the NYPD.
"In this case, the images that we shared with the public were spread far and wide, and the tips we received led to the recovery of crucial evidence," Commissioner Tisch said.
"We should never underestimate the power of the public to be our eyes and our ears in these investigations."
After the arrest, a spokesperson for UnitedHealth thanked law enforcement and requested privacy for the victim's family.
"Our hope is that today's apprehension brings some relief to Brian's family, friends, colleagues and the many others affected by this unspeakable tragedy," the spokesperson told the ABC.
