In the early morning of Dec. 4, 2024, Brian Thompson, the chief executive of UnitedHealthcare, was walking just outside the Hilton Hotel in Midtown Manhattan, where he was attending a conference. He soon collapsed to the ground with gunshot wounds to his back and right leg.

Responding police officers locked down the bustling intersections surrounding the crime scene. Traffic was rerouted and investigators scoured New York City for evidence of the gunman, even sending divers into a lake in Central Park.

The shooting led to a national manhunt, with multiple law enforcement agencies searching for clues and retracing the steps of the hooded shooter.

After five days, Luigi Mangione, a 26-year-old from Maryland, was arrested at a McDonald’s in Altoona, Pa. He was identified, according to the restaurant manager, by his distinct bushy eyebrows, which had been visible in surveillance footage from New York.

Mr. Mangione was subsequently charged with both federal and state crimes connected to the killing. On Friday, however, he pleaded guilty to the federal stalking charges. His state trial, on charges that include second-degree murder, is scheduled to begin next month.

Dec. 4, 2024: Brian Thompson, the chief executive of UnitedHealthcare, is shot to death as he walks outside the New York Hilton Midtown in Manhattan. Hiding between parked cars nearby was a masked gunman holding a semiautomatic pistol with a silencer. Though the gun appears to jam, the shooter clears the chamber and fires off a succession of shots, striking Mr. Thompson. A multiagency manhunt begins soon after.

Dec. 9, 2024: Mr. Mangione is arrested at a McDonald’s in Altoona, Pa. Customers reported to the restaurant manager that a customer had matched the description of the Manhattan shooter. The police recover Mr. Mangione’s backpack, which includes a 3-D-printed ghost gun, a silencer and a written manifesto, among other items. He is arraigned in Blair County and charged with five crimes in Pennsylvania, including carrying a gun without a license, forgery and falsely identifying himself to authorities. Those charges are still pending.

Dec. 17, 2024: A grand jury in Manhattan indicts Mr. Mangione on first-degree murder charges, along with second-degree murder in furtherance of terrorism and other counts. The charges carry a maximum penalty of life in prison without parole.

Dec. 19, 2024: Federal prosecutors unseal separate charges against Mr. Mangione that include using a firearm to commit murder along with two stalking counts and a firearms offense. The federal charges open the door to the death penalty.

Dec. 23, 2024: After Mr. Mangione is extradited to New York from Pennsylvania, he is arraigned on the charges in State Supreme Court. He pleads not guilty. A state judge later dismisses the terrorism-related charges.

February 2025: Contributions to Mr. Mangione’s defense fund, set up by his attorneys, reach $500,000. As Mr. Mangione’s cases wind their way through state and federal courts, some Americans come to see him as taking a stand against a bureaucratic health care system. Mr. Mangione’s supporters start rallying outside his court appearances.

April 1, 2025: Attorney General Pam Bondi announces that the Department of Justice will seek the death penalty in Mr. Mangione’s federal case. Ms. Bondi says her decision came after “careful consideration” and was in line with President Trump’s executive order directing the Justice Department to renew death penalty requests.

April 17, 2025: A federal grand jury indicts Mr. Mangione on four charges, paving the way for a separate federal trial. The charges include using a firearm to commit a murder, which carries the death penalty. By April, Mr. Mangione’s defense fund has topped $900,000 in donations.

April 25, 2025: Mr. Mangione pleads not guilty at a hearing in federal court. Judge Margaret M. Garnett admonishes the Justice Department for making what she said were political comments on the case, and orders Ms. Bondi to refrain from publicly discussing it, which she had done earlier that month on Fox News. During the hearing, Mangione supporters surround the court building.

Sept. 16, 2025: The state terrorism charges against Mr. Mangione are dismissed. The judge in the case, Gregory Carro, says the evidence behind the charges — including a first-degree murder charge that could put Mr. Mangione behind bars for life — was “legally insufficient.” Mr. Mangione still faces nine counts at a trial scheduled for the next year.

Sept. 24, 2025: Judge Garnett admonishes Trump officials for what she describes as inappropriate and politicized comments, which she says violate her April order. The comments began soon after Mr. Trump said on Fox News that Mr. Mangione had “shot someone in the back as clear as you’re looking at me.” Karoline Leavitt, the White House press secretary, would go on to refer to Mr. Mangione at a news conference as a “left-wing assassin.”

December 2025: Three weeks of evidentiary hearings take place at State Supreme Court, a trial court. The proceedings revolve around the contents of a backpack taken from Mr. Mangione when he was arrested in Pennsylvania. His defense lawyers claim that the police did not have a warrant to search Mr. Mangione’s bag, nor did they properly read him his Miranda rights.

Jan. 30, 2026: Judge Garnett dismisses two federal charges against Mr. Mangione, including one that carried the death penalty. Mr. Mangione still faces two counts of stalking that resulted in death, which carry a maximum penalty of life in prison.

February 2026: Justice Carro, the judge in the state case, sets a trial date for June 2026 after federal prosecutors say they will begin jury selection in their own case in September. Federal and state prosecutors are locked in a tug of war over who will try Mr. Mangione first. Both parties eventually push their trial dates back, with state prosecutors set to go first in September.

May 18, 2026: In a partial victory for state prosecutors, Justice Carro rules that some of the belongings found in Mr. Mangione’s backpack, including a ghost gun and a notebook containing a manifesto decrying the health care industry, can be used as evidence.

June 18, 2026: In an abrupt reversal, Mr. Mangione’s lawyers quickly withdraw their intent to use emotional disturbance as a line of defense in his state case. Such an argument would amount to an admission that Mr. Mangione killed Mr. Thompson. Under New York law, if defense lawyers can prove that strong emotions led to a “profound loss of self-control,” the highest charge a defendant can face is manslaughter.

Aug. 11, 2026: Justice Carro rules that the jurors in Mr. Mangione’s state trial will remain anonymous. The decision comes in response to a request from prosecutors, who said the publicity surrounding the trial — along with threats already made to members of the court and certain witnesses — could taint the jury pool.

Aug. 14, 2026: Mr. Mangione, now 28, pleads guilty before Judge Garnett in federal court to the stalking charges. His defense team files a motion arguing that his state charges should be dismissed because of New York’s double jeopardy laws. It is unclear whether such an argument will hold up in court.