ALTOONA, Pa. (AP) — The gun found on the man charged with killing United Healthcare’s CEO matched shell casings found at the site of the shooting, New York City’s police commissioner said Wednesday as authorities scrutinized evidence and the suspect’s experiences with the victim’s industry.

Luigi Mangione ’s fingerprints also matched a water bottle and a snack bar wrapper that police found near the scene in midtown Manhattan, Commissioner Jessica Tisch said at an unrelated news conference. Police had said earlier that they believed the gunman bought the items at a nearby coffee shop while awaiting his target.

Mangione, 26, remained jailed without bail Wednesday in Pennsylvania, where he was arrested and initially charged with gun and forgery offenses. Manhattan prosecutors were working to bring him to New York to face a murder charge in the death of Brian Thompson, the leader of the United States’ biggest health insurer.

Mangione’s lawyer has cautioned the public against prejudging the case.

While the case is in early stages, police believe the suspect may have been motivated by animus toward the health care industry.

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Investigators are looking into an accident that injured Mangione’s back and sent him to an emergency room on July 4, 2023, police said Wednesday. They’re scrutinizing his Facebook page, where he posted X-rays of numerous screws that were inserted into his spine. And police are studying his writings about the injury and his disdain for corporate America and the U.S. health care system.

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

The letter 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.

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

In his first public words since his arrest, Mangione shouted about an “insult to the intelligence of the American people” on his way into court Tuesday.

At a brief hearing, defense lawyer Thomas Dickey said that he didn’t believe there was evidence to support a forgery charge and questioned whether the gun allegation amounts to a crime. Dickey also said Mangione would contest his extradition to New York and wanted 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 the gun 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.

There were no fingerprints on the ammunition found at the shooting scene, but work is ongoing to analyze a print on cellphone left nearby, police said Wednesday.

Police are continuing to search for more surveillance video showing Mangione’s movements in New York between Nov. 24, when they say he arrived in the city, and the shooting. From video collected already, investigators determined the suspect quickly fled the city, likely by bus, after the killing.

His movements afterward are unclear, but authorities believe he took steps to stay off the radar. Prosecutors said at Mangione’s Pennsylvania hearing this week that when arrested, he had what are known as Faraday bags for his cellphone and laptop to block signals authorities can use to track electronic devices.

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 “shocked and devastated” at his arrest.

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Sisak reported from New York. Associated Press writer Jennifer Peltz contributed.