The day after a masked gunman killed the CEO of UnitedHealthcare in New York City, police in San Francisco gave the FBI a potentially valuable tip about the identity of the suspect: He looked like a man who had been reported missing to them the previous month, Luigi Mangione.

San Francisco police provided Mangione’s name to the FBI on Dec. 5, according to a law enforcement official was not authorized to publicly discuss details of the investigation and spoke to The Associated Press on the condition of anonymity.

That was the day the NYPD released surveillance images showing the face of the suspected shooter as he checked into a Manhattan hostel.

“Among multiple tips received by FBI New York from the public and law enforcement regarding the homicide in Midtown Manhattan on December 4, 2024, a tip was received from the San Francisco Police Department regarding the possible identity of the suspect,” the FBI confirmed in a statement Friday.

The FBI statement didn’t provide further detail about the nature of the tip or say when it was received but said agents in New York had “conducted routine investigative activity and referred this and other leads to the New York City Police Department.”

Mangione was arrested Monday, Dec. 9, after an employee at a McDonald’s in Altoona, Pennsylvania, phoned police saying that there was a person eating breakfast in the restaurant who looked like the person being sought as the gunman.

The NYPD's chief of detectives, Joseph Kenny, said at the time that the department's investigators didn't have Mangione's name until he turned up in that McDonald's.

A message seeking comment was left with the NYPD Friday.

The San Francisco department's tip to the FBI was first reported by the San Francisco Chronicle.

UnitedHealthcare CEO Brian Thompson was ambushed and fatally shot outside a hotel where his company was holding its annual investor conference.

The leader of the insurer's parent company, UnitedHealth Group, described Thompson as kind and brilliant Friday in a guest essay published in The New York Times.

UnitedHealth Group CEO Andrew Witty conceded that the patchwork U.S. health system “does not work as well as it should” but said Thompson cared about customers and was working to make it better.

The killing has been viewed as a violent expression of widespread anger at the insurance industry. Witty said people in the company were struggling to make sense of the killing, as well as the vitriol and threats directed at colleagues.

Police have said that Mangione was found with a gun that matched shell casings found at the scene of the shooting and a three-page letter in which he lamented the high cost of health care in the U.S. and singled out UnitedHealthcare for its profits and size. The company, a division of UnitedHealth Group, is the largest U.S. health insurer. Mangione is currently being held in Pennsylvania and intends to plead not guilty to a murder charge in New York, his lawyer has said.

Witty said he understood people's frustration but described Thompson as part of the solution.

Thompson never forgot growing up in his family's farmhouse in Iowa and focused on improving the experiences of consumers.

“His dad spent more than 40 years unloading trucks at grain elevators. B.T., as we knew him, worked farm jobs as a kid and fished at a gravel pit with his brother. He never forgot where he came from, because it was the needs of people who live in places like Jewell, Iowa, that he considered first in finding ways to improve care,” Witty wrote.

Witty said his company shares some responsibility for lack of understanding of coverage decisions.

"We know the health system does not work as well as it should, and we understand people’s frustrations with it. No one would design a system like the one we have. And no one did. It’s a patchwork built over decades,” Witty wrote. “Our mission is to help make it work better.”

He said it was unfair that the company's workers had been barraged with threats, even as they grieved the loss of a colleague.

“No employees — be they the people who answer customer calls or nurses who visit patients in their homes — should have to fear for their and their loved ones’ safety,” he wrote.

A woman in Lakeland, Florida, was charged this week with threatening a worker at her own health insurance company, Blue Cross Blue Shield, during a phone call. Police said she cited words Thompson’s killer wrote on shell casings and said “you people are next” during the recorded call.

Police say the shooter waited outside the hotel, where the health insurer was holding its investor conference, early on the morning of Dec. 4. He approached Thompson from behind and shot him before fleeing on a bicycle.

Mangione is fighting attempts to extradite him to New York so he can face a murder charge in Thompson’s killing.t corporation in America, which would make it the largest healthcare organization in America. So that’s possibly why he targeted that company,” said Kenny.

UnitedHealthcare is in the top 20 largest U.S. companies by market capitalization but is not the fifth largest. It is the largest U.S. health insurer.

Mangione remains jailed without bail in Pennsylvania, where he was arrested Monday after being spotted at a McDonald's in the city of Altoona, about 230 miles (about 370 kilometers) west of New York City. His lawyer there, Thomas Dickey, has said Mangione intends to plead not guilty. Dickey also said he has yet to see evidence decisively linking his client to the crime.

Mangione's arrest came five days after the caught-on-camera killing of Thompson outside a Manhattan hotel.

Police say the shooter waited outside the hotel, where the health insurer was holding its investor conference, early on the morning of Dec. 4. He approached Thompson from behind and shot him before fleeing on a bicycle through Central Park.

Mangione is fighting attempts to extradite him back to New York so that he can face a murder charge in Thompson's killing. A hearing has been scheduled for Dec. 30.

The 26-year-old, who police say was found with a “ ghost gun ” matching shell casings found at the site of the shooting, is charged in Pennsylvania with possession of an unlicensed firearm, forgery and providing false identification to police.

Mangione is an Ivy League graduate from a prominent Maryland real estate family. In posts on social media, Mangione wrote about experiencing severe chronic back pain before undergoing a spinal fusion surgery in 2023. Afterward, he posted that the operation had been a success and that his pain had improved and mobility returned. He urged others to consider the same type of surgery.

On Wednesday, police said investigators are looking at his writings about his health problems and his criticism of corporate America and the U.S. health care system.

Kenny said in the NBC interview that Mangione's family reported him missing to San Francisco authorities in November.