NEW YORK — The killing lasted only seconds. The argument it unleashed has lasted nearly two years. On the morning of Dec. 4, 2024, UnitedHealthcare chief executive Brian Thompson was walking toward an investor conference at the New York Hilton Midtown when a gunman approached and shot him. Surveillance footage of the attack quickly spread across the country, setting off a nationwide manhunt and transforming what might otherwise have been remembered as the murder of a corporat