The gun found on the suspect in the killing of United Healthcare’s CEO matched shell casings found at the site of the shooting, New York City’s police commissioner said Wednesday.

Suspect Luigi Mangione’s fingerprints also matched a water bottle and a protein bar wrapper that police found near the scene and that officials say the gunman purchased at a nearby coffee shop while awaiting his target, Commissioner Jessica Tisch said at an unrelated news conference.

The 26-year-old Mangione’s was charged with murder in the shooting last week in midtown Manhattan of Brian Thompson, who led the United States’ largest medical insurance company.

Authorities have said that writings found in Mangione's possession hinted at a hatred of corporate greed.

They’ve recovered a spiral notebook that Mangione kept, along with a three-page handwritten letter found when he was arrested, a law enforcement official said Wednesday. Police have not disclosed what was in the notebook.

The letter, found when Mangione was arrested Monday in Altoona, Pennsylvania, 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. The official wasn’t authorized to disclose information about the investigation and spoke to The Associated Press on condition of anonymity.

Kenny told CBS New York that the motive might have been related to an accident that sent Mangione to an emergency room on July 4, 2023.

A law enforcement bulletin obtained by the AP earlier this week said the letter expressed anger with what Mangione called “parasitic” health insurance companies and a disdain for corporate greed and power. The prep school and Ivy League graduate wrote that the U.S. has the most expensive health care system in the world and that profits of major corporations continue to rise while life expectancy doesn't, according to the bulletin.

In his first public words since his arrest, Mangione emerged from a patrol car Tuesday shouting about an “insult to the intelligence of the American people” while deputies pushed him into a courthouse. Mangione remained jailed without bail in Pennsylvania, where he was initially charged with gun and forgery offenses.

Manhattan prosecutors were working to bring Mangione to New York. At a brief hearing Tuesday in Pennsylvania, defense 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,” Dickey said afterward. “He’s presumed innocent. Let’s not forget that.”

Mangione was arrested in Altoona, about 230 miles (about 370 kilometers) west of New York City, after a McDonald’s customer recognized him and notified an employee, authorities said.New York police officials have said Mangione was carrying a gun like the one used to kill Thompson and the same fake ID the suspected shooter had used to check into a New York hostel, along with a passport and other fraudulent IDs.

Thompson, 50, was killed Dec. 4 as he walked alone to a Manhattan hotel for an investor conference. From surveillance video, New York investigators determined the shooter 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 Tuesday that when arrested, he had bags for his cellphone and laptop that prevent such devices from transmitting signals that authorities can use to track them.

Mangione, a grandson of a well-known Maryland real estate 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 bunked 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.”