By Lauren Mascarenhas, Mark Morales, Amanda Musa, CNN

(CNN) — A supervisor at the Las Vegas casino where Shane Devon Tamura worked legally purchased the gun used in the Midtown Manhattan shooting and sold it to him for $1,400, a law enforcement official told CNN Wednesday.

Tamura, 27, walked into 345 Park Avenue on Monday evening carrying an M4 assault-style rifle and opened fire, police said, killing four people and injuring another before he died by suicide.

After an interview with the supervisor, investigators learned that the supervisor had bought the assault rifle in August 2024 and assembled it before selling it to Tamura, two law enforcement officials said. New York City Police Commissioner Jessica Tisch said in a video posted Tuesday, before investigators had questioned the supervisor, that the weapon was “assembled by Mr. Tamura using a lower receiver purchased by an associate.”

The same person also sold Tamura the car that the shooter used to drive to New York to commit the crime on Monday, the official said. The supervisor is cooperating with authorities, the official said.

CNN has reached out to the casino for comment.

Tamura’s parents are also talking to investigators and are said to be cooperating as well, the official added.

The attack at the Park Avenue skyscraper is now the deadliest event recorded in New York City since at least 2013, according to data from the Gun Violence Archive.

A note found in the gunman’s pocket claimed he was suffering from CTE, a disease linked to head trauma – one that’s often associated with football players – and expressed grievances with the NFL, a source told CNN.

Tamura apologized to a man in the note found in his back pocket, and that man is believed to be the supervisor, another law enforcement official said.

Investigators believe Tamura was headed for the NFL offices at the time of the shooting, but he took the wrong elevator, New York City Mayor Eric Adams said.

For some, the stark image of the shooter walking in Midtown Manhattan, rifle in hand, harkened back to another high-profile shooting in the bustling business district: the targeted killing of the UnitedHealthcare CEO in December, by a gunman who expressed frustration with the healthcare industry.

The victims of Monday’s attack included an off-duty New York police officer, who was the father of two young sons, with a third child on the way; an executive at investment firm Blackstone; a security guard described by his union as a “New York hero”; and a Cornell graduate who worked for the building owner.

An NFL employee was also seriously injured in the shooting.

Purchases at a Vegas gun show

As the city mourns those killed, investigators are probing the weapons retrieved from the scene and digging into the gunman’s history.

Hours after the shooting, Las Vegas Police Crimestoppers received a tip from a licensed firearms dealer saying he saw Tamura at a Las Vegas gun show in June, a senior law enforcement official told CNN.

The gun dealer says he remembered Tamura after he saw his picture on the news and recalled that he sought to buy an aftermarket trigger assembly for an M4 rifle, the official said.

An aftermarket trigger assembly can replace the factory trigger with one designed for a specific kind of shooting, whether rapid-fire, close combat, or long-range accuracy.

Tamura returned the trigger assembly the next day, saying he needed the money back to buy 500 rounds of .223 ammunition – the same kind of ammunition used in the New York shooting, according to the official.

The gun dealer told police Tamura came back the next day with additional funds and re-purchased the trigger assembly, the official said.

New York officials call for gun reform

Mayor Adams and New York Gov. Kathy Hochul attended a multi-faith prayer vigil on Tuesday, both advocating for gun reform in their remarks.

“We cannot respond to senseless gun laws through vigils,” Adams said. “It must be responded through legislation. It is time to turn the corner of a society where automatic weapons are as easy to get as a cell phone.”

Hochul reiterated her call for Congress to address the issue.

The governor spoke about her conversation with the widow of slain New York Police Department Officer Didarul Islam.

“I spoke to the young widow, a mother of two expecting her third child. I tried to convey, again, that sense of compassion all of us as human beings feel,” Hochul said during a vigil for the victims of the mass shooting. “I said, ‘Is there anything we can do for you?’ And in her broken English, she just said: ‘Pray for us.’”

Islam, 36, was a Bangladeshi immigrant hailed as a hero by city officials. He was off duty but in uniform working security in the building when he was killed, Tisch said.

A funeral for Islam is scheduled for Thursday morning in the Bronx, the Police Benevolent Association of the City of New York said in an X post Wednesday.

Tisch said Islam represents the best of New York City.

“He served this city with quiet strength and unwavering purpose,” she said. “He didn’t ask for attention. He didn’t ask for praise. He simply showed up, tour after tour, and did the work that holds this city together.”

Tisch also spoke about the other victims, including her “beautiful friend Wesley” LePatner, a Blackstone employee killed in the attack.

LePatner is survived by her husband and children, Blackstone said Tuesday.

LePatner’s family called her “the most loving wife, mother, daughter, sister and relative, who enriched our lives in every way imaginable.”

Another victim, Julia Hyman, was an associate at Rudin Management, the real estate firm that owns the Park Avenue building. Cornell dean and professor Kate Walsh described Hyman, a 2020 graduate, as “an extraordinary student.”

Hyman’s funeral was held Wednesday at Central Synagogue in her native Manhattan, according to the temple’s website.

Aland Etienne, the security officer who was killed, was “a light” in his family’s lives, they said.

“Every time a security officer puts on their uniform, they put their lives on the line. Their contributions to our city are essential, though often unappreciated. Aland Etienne is a New York hero. We will remember him as such,” said Manny Pastreich, President of 32BJ SEIU, a national union representing property service workers.

The NFL employee who was seriously injured in the shooting was in the hospital Tuesday in stable condition.

“Our thoughts and prayers remain especially with our colleague who was impacted,” NFL Commissioner Roger Goodell said Tuesday in a statement to his employees obtained by CNN. “He is currently surrounded by his family and members of the NFL community, and we are all continuing to hope for and support his full recovery,”

The NFL’s New York office will be closed until at least the end of next week, Goodell said.

The investigation continues

?New York City’s chief medical examiner’s office will test Tamura’s remains for CTE, an office spokesperson told CNN Tuesday. The only way to diagnose the disease is through an autopsy of the brain.

Tamura was a competitive football player in his youth, sources said.

Investigators are also examining how Tamura made his way from Las Vegas to New York City, with an AR-15 style weapon.

The New York Police Department said it is sending investigators to Las Vegas, where the gunman lived, to learn more about a possible motive.

A search of the gunman’s car turned up a host of items, including additional ammunition, another loaded weapon, headphones potentially used for target practice, two cell phones, the antidepressant Zoloft and cannabis, a law enforcement source told CNN.

Another note found in the gunman’s apartment, directed at his mother, read, “When I look into yours and dad’s eyes … all I see is disappointment,” CNN Chief Law Enforcement and Intelligence Analyst John Miller said.

Tamura was placed on psychiatric hold in 2022 and 2024, according to a law enforcement official briefed on the situation.

This story has been updated with additional information.

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CNN’s Amanda Musa, Emma Tucker, Sara Smart, Mark Morales, Rebekah Riess, Jessie Yeung, Jill Martin and Taylor Romine contributed to this report.