Mangione had initially pleaded not guilty in both the federal and state cases against him for the shooting death of Thompson.
At a hearing in Manhattan federal court on Friday, Mangione’s lawyers announced that he intended to plead guilty to the two federal charges against him.
Wearing a beige prison outfit, Mangione appeared solemn and serious throughout the hearing.
Reading a statement aloud to the court, he admitted to planning the attack ahead of time, crossing state lines with the intent to kill and using a gun he printed on a 3-D-printer and equipped with a silencer and magazine.
He told the court he was driven to kill Thompson because of his experience with the healthcare system “after years of enduring severe pains from a broken back”.
Mangione stated that he had learned UnitedHealthcare would hold an annual investor conference in Manhattan in December 2024.
He then travelled to New York for the event, he told the court.
He also said he emailed UnitedHealthcare prior to the conference “posing as an investor” and asking questions about the event.
“I emailed UnitedHealthcare with the intent to shoot Brian Thompson,” Mangione said in his statement. “On the morning of Dec. 4, 2024 I shot Mr. Thompson in Manhattan in his back.”
The sentencing for the federal charges is scheduled for 18 December.
Brian Thompson’s family said in a statement that they will continue to seek justice in both New York state and Pennsylvania, where Mangione was arrested.
“While nothing will ease the pain of losing him, we are grateful that the federal justice system has held the person responsible for this heinous act accountable.
“Now we look to the court to ensure that sentencing reflects the severity of this crime,” the family added.