THE GUN FOUND on the suspect in the killing of UnitedHealthcare’s chief executive matches shell casings found at the crime scene, New York’s police commissioner said on Wednesday.

Commissioner Jessica Tisch also said lab results matched suspect Luigi Mangione’s prints to a water bottle and protein bar wrapper found near the scene of the killing.

Authorities were also analysing a fingerprint on a mobile phone found after the killing of Brian Thompson as Mangione fought being sent from a Pennsylvania jail to New York to face a murder charge.

The New York Police Department’s top detective, Joseph Kenny, told CBS New York on Tuesday that no prints were found on bullets that killed Thompson, but one fingerprint on a mobile phone was recovered.

He said the evidence was being processed and did not say whether it appeared to match Mangione, the 26 year-old charged over the shooting last week in midtown Manhattan.

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

They have 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 on 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 was not authorised 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 hospital 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 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,” Dickey said afterwards. “He’s presumed innocent. Let’s not forget that.”

Mangione was arrested in Altoona, about 230 miles (about 370km) 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 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.

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”.