Luigi Mangione has been charged with first degree murder over the killing of healthcare CEO Brian Thompson.
Mr Mangione has been indicted on one charge of first-degree murder and two counts of second-degree murder, one of which is charged as killing as an act of "terrorism", New York District Attorney Alvin Bragg said.
As Mr Bragg announced the charges, he called the shooting a "frightening, well-planned and targeted murder".
Mr Mangione is due to appear for a court hearing on December 19 over whether he will be extradited to New York, according to CBS News.
Mr Mangione, who was arrested on last Monday in a McDonald's in Pennsylvania, was was found with a gun, mask and writings linking him to the ambush of Mr Thompson.
His lawyer, Thomas Dickey, said he plans to fight the extradition and maintains he has not seen evidence that links Mr Mangione's gun with the crime.
Police earlier recovered a spiral notebook that Mangione kept, along with a three-page handwritten letter found when he was arrested, a police official said on Wednesday. Police have not disclosed what was in the notebook.
The letter, found when Mangione was arrested, teased the possibility that clues to the attack – "some straggling notes and to do lists that illuminate the gist of it" – could be found in the notebook, the law enforcement official said.
A law enforcement bulletin obtained by the AP last week said the letter expressed anger with what Mangione called "parasitic" health insurance companies and a disdain for corporate greed and power.
The Ivy League graduate wrote that the US has the most expensive healthcare system in the world and that profits of major corporations continue to rise while life expectancy does not, according to the bulletin.
In his first public words since his arrest, Mangione emerged from a patrol car on Tuesday shouting about an "insult to the intelligence of the American people" while officers pushed him into a court building. Mangione remained jailed without bail in Pennsylvania, where he was initially charged with gun and forgery offences.
Manhattan prosecutors were working to bring Mangione to New York. At a brief hearing on Tuesday in Pennsylvania, defence lawyer Thomas Dickey said Mangione will not waive extradition and instead wants a hearing on the issue.
"You can't rush to judgment in this case or any case," Mr Dickey said afterwards. "He's presumed innocent. Let's not forget that."
Mangione was arrested in Altoona, Pennsylvania, about 230 miles west of New York City, after a McDonald's customer recognised him and notified an employee, authorities said.
New York police officials have said Mangione was carrying a gun like the one used to kill Mr Thompson and the same fake ID the suspected gunman had used to check in to a New York hostel, along with a passport and other fraudulent IDs.
Mr Thompson, 50, was killed on December 4 as he walked alone to a Manhattan hotel for an investor conference. From surveillance video, New York investigators determined the gunman quickly fled the city, likely by bus.
His movements afterward are unclear, but authorities believe he took steps to stay off the radar. Prosecutors said at his Pennsylvania hearing on Tuesday that when arrested, he had bags for his mobile phone and laptop that prevent such devices from transmitting signals that authorities can use to track them.
Mangione, a grandson of a well-known Maryland property developer and philanthropist, had a graduate degree in computer science and worked for a time at a car-buying website.
During the first half of 2022, he stayed at a "co-living" space in Hawaii, where those who knew him said he suffered from severe and sometimes debilitating back pain.
His relatives have said in a statement that they are was "shocked and devastated" at his arrest".