A man who shot dead an American health insurance executive in the street has been charged with first-degree murder

A grand jury in the United States has formally indicted the man who shot dead an American health insurance executive in the street in New York on first-degree murder charges.

Luigi Mangione, 26, was formally charged Tuesday in New York with being a terrorist who saw the killing of UnitedHealth CEO Brian Thompson as a legitimate political act, the New York Times reported.

"This was a horrific, well-planned, targeted murder designed to shock, concern and intimidate," Manhattan District Attorney Michael Bragg said at a news conference.

Mangione also faces two counts of second-degree murder and firearms charges in New York.

Thompson, 50, has been an executive at UnitedHealth Group, the nation's largest health insurer, for about 20 years. In the early morning of December 4, he was shot and killed outside the Hilton Hotel in downtown New York.

Mangione was caught at a McDonald's in Altoona, Pennsylvania, in possession of multiple fake ids and a 3D-printed handgun with a silencer.