NEW YORK (AP) — Luigi Mangione pleaded guilty on Friday to federal stalking charges in the killing of UnitedHealthcare CEO Brian Thompson, admitting matter-of-factly that he trailed the executive to an investor conference in 2024 and gunned him down on a New York City street.

Mangione, 28, said he even used a ruse to glean information about the event, contacting the health insurance company ahead of time under the guise of being an investor at a multibillion-dollar firm.

"On the morning of Dec. 4, 2024, I shot Mr. Thompson in Manhattan, and he died,” Mangione told the court as Thompson's wife, Paulette, took several deep breaths and repeatedly wiped tears from her eyes. A supporter put an arm around the wife and held her tight.

Mangione is set for sentencing Dec. 18. When U.S. District Judge Margaret M. Garnett asked whether he understood that he could spend the rest of his life in prison, Mangione answered neutrally: “Yes.”

Mangione entered the plea at a hastily scheduled hearing in Manhattan federal court, resolving one of two cases against him in connection with Thompson’s death. Mangione's lawyers are now seeking to have his separate New York state murder case thrown out on double jeopardy grounds.

“Mr. Mangione has accepted full responsibility for the death of Brian Thompson,” defense lawyer Karen Friedman said outside court, arguing that her client shouldn't face two prosecutions over a “single tragic event.”

Surveillance video of the ambush showed a masked gunman shooting Thompson, 50, from behind. Police say “delay,” “deny” and “depose” were written on the ammunition, mimicking a phrase used to describe how insurers avoid paying claims. That detail — and revelations that Mangione's private writings lambasted health insurers as greedy, according to authorities — made the case a fulcrum for debate about the industry and made Mangione a cause célèbre for some of its critics.

Mangione told the court Friday that he pursued Thompson “after years of enduring severe pain from a broken back and navigating the obstacles of the health insurance system.”

Mangione never was a UnitedHealthcare customer, according to police and the company. A University of Pennsylvania graduate from a wealthy Maryland family, he was arrested five days after the shooting, when he was spotted at a McDonald’s in Altoona, Pennsylvania. It's about 230 miles (370 kilometers) west of Manhattan.

Thompson led one of the United States' largest health insurers, but he wasn't well known outside the industry. Trained as an accountant, he had worked at parent company UnitedHealth Group Inc. for 20 years and became CEO of its insurance arm, UnitedHealthcare, in 2021. He and his wife have two sons, who were in high school when their father was killed.

Both the federal and state cases could lead to a life prison sentence for Mangione. A federal judge earlier this year tossed out additional charges that could have exposed him to a potential death penalty.

Mangione had complained about the prospect of two trials, telling a judge in February: “It’s the same trial twice. One plus one is two. Double jeopardy by any commonsense definition.”

Under New York law, a state prosecution could potentially be barred if the federal case is resolved first.

The state’s double jeopardy protections kick in if a jury has been sworn in a prior prosecution, such as a federal case, or if that prosecution ends in a guilty plea. Mangione’s cases involve different charges arising from the same course of conduct.

In a letter last month, state prosecutors objected to the possibility of a guilty plea in the federal case wiping out the state case.

Garnett has delivered some setbacks to the defense, including ruling in January that prosecutors could use items collected from Mangione’s backpack during his arrest as evidence against him.

They included a 3D-printed pistol that investigators said matched the one used to kill Thompson and a notebook in which authorities say Mangione described his intent to kill an insurance executive.

In June, Mangione’s lawyers said they would pursue a psychiatric defense in the state case but reversed course a day later. The defense, involving claims that he was suffering from extreme emotional disturbance at the time of the killing, isn’t allowed in federal court.