LAS VEGAS — The gunman who killed four people before taking his own life in a midtown Manhattan office building that houses the NFL’s headquarters had for years sought medical help for frequent, debilitating headaches — including receiving injections in the back of his head, a person close to the man’s family told ESPN.

Shane Tamura, a 27-year-old Las Vegas casino worker, had regularly met with doctors, including a neurologist, and received yearly MRI exams and various treatments seeking to diagnose the cause and stop the pain, said the source who spoke on the condition of anonymity.

Tamura began having headaches while he was playing high school football in Southern California, the source said, and they continued into adulthood. Tamura took acetaminophen or ibuprofen, the source said, but soon after moving to Las Vegas in 2019 searched for more help. Doctors prescribed various medications for Tamura to try to find groupings that could offer relief, the source said.

“As it got worse and worse,” the source said, “it was like, ‘OK, I have to get doctors’ help now.'”

Four people, including an off-duty New York City police officer, were killed in the shooting, and an NFL employee was seriously injured. The source close to the family told ESPN that Tamura’s immediate family is grieving, “especially for the innocent lives that are lost.”

In the week after the shooting, while funerals were being held in New York for the victims and law enforcement authorities in Las Vegas were executing search warrants, details emerged about Tamura — his years playing football at two Los Angeles-area high schools, his history with mental health, his time with a private security firm, working a surveillance job in a Las Vegas casino and a run-in with a different casino’s security when he refused to leave while trying to collect winnings.

Tamura began playing tackle football at age 6 and continued through high school. Friends who knew him a decade ago when he was a popular running back with star potential told ESPN they had lost touch and wondered what he did after moving away. Because of his size — he was listed in high school at 5-foot-7, 140 pounds — the source close to the family said he didn’t ponder ambitions of playing in the NFL.

Investigators said they believed Tamura was trying to reach the NFL’s headquarters but took the wrong elevator. A note found by police in Tamura’s wallet suggested he had a grievance against the NFL over a claim that he had chronic traumatic encephalopathy. In the note, he repeatedly said he was sorry and asked that his brain be studied for CTE, according to authorities and photos of the note.

The source told ESPN that during the time Tamura lived in Nevada, he had been treated for depression and twice been held involuntarily for mental health reasons. In Nevada, a person experiencing a mental health crisis can be held and evaluated at a hospital or crisis center for up to 72 hours if they are likely to be a danger to themselves or others.

The source didn’t remember Tamura expressing anger toward the NFL but recalled how Tamura would talk about younger players needing better equipment and more safety. At least once, the source said, Tamura said he believed he had CTE but also knew that it could be diagnosed only posthumously.

Brain experts who spoke with ESPN have cautioned against drawing direct connections between the shooting and the disease. CTE is a degenerative brain disease that can be diagnosed only after someone has died. It has been linked to concussions and other repeated head trauma common in contact sports such as football. The experts told ESPN it could take weeks to learn whether Tamura had CTE.

The source close to the family told ESPN that Tamura would sometimes go to work on an overnight shift in surveillance at the Horseshoe Casino and Hotel in Las Vegas and return home to sleep, placing an ice pack on his forehead because of headaches. The injections in his head at times reduced the pain, the source said, but it persisted. Doctors sometimes treat severe headaches with nerve blocks, injecting steroids and pain medicine near the base of the skull. The source said the hope was that medical research on Tamura’s brain would show what he suffered from and help to find answers.

The weekend before the shooting, authorities have said, Tamura drove from Las Vegas to New York, arriving on Monday. He double-parked a BMW outside 345 Park Avenue and, around 6:30 p.m. ET, walked across the building’s entry plaza with an assault-style rifle. It was just past peak rush hour in one of the busiest areas of America’s largest city.

Once in the lobby of the 44-story skyscraper, Tamura shot Didarul Islam — the off-duty police officer — and a woman fleeing for cover. He shot a second security guard and another man in the lobby before taking the elevator. Investigators said they believed he was trying to reach the NFL offices, but he arrived on the 33rd floor, where he shot a woman before shooting himself in the chest with the rifle.

The investment firm Blackstone confirmed that one of its employees, real estate executive Wesley LePatner, was among those killed. Julia Hyman, who worked as an associate at Rudin Management, and security officer Aland Etienne also were killed, according to the City of New York Office of Chief Medical Examiner.

In a memo sent to NFL employees Tuesday, commissioner Roger Goodell said “our thoughts and prayers remain especially with our colleague.” He later called the shooting “an attack on humanity.”

Elijah McCormick, who described Tamura as a childhood best friend, said he wished he would have been able to speak with Tamura “before he did anything.” The two met when they were 8 years old and played football at Golden Valley High School in Santa Clarita, California. They hadn’t spoken since.

“Just would have told him to tell me what’s on his mind,” McCormick said. “Hopefully, I could figure out the s— together with him.”

Five former football teammates who spoke with ESPN all played together at Golden Valley and were friendly off the field while growing up in the Santa Clarita Valley, about 30 miles north of downtown Los Angeles.

One former Golden Valley teammate described Tamura as a “goofball,” and another remembered his rumbling staccato laugh and the way he would dash away after a good-natured prank.

Tamura and his parents, Terence and Michelle, and his older brother, Terry, lived in Canyon Country, a neighborhood on the eastern edge of the city of Santa Clarita. His father was an officer in the Los Angeles Police Department — he retired in good standing on Aug. 5, 2017, according to a department spokesperson — and his brother also played football. There was no answer Thursday when a reporter knocked on the door at the home of Tamura’s parents in Las Vegas.

Tamura took up sports in grade school. McCormick recalled days playing football and in a travel basketball league. Later, Tamura was a sprinter for the track team and loved boxing.

“He was a very sport-oriented kind of guy,” former teammate Duke Castillo said.

At Golden Valley, Tamura was known for his speed. “This dude ran like a 4.4,” Castillo said. By his junior year, Tamura made varsity and rushed for 774 yards and 11 touchdowns. He was a 140-pound blur in the open field. Golden Valley won three games.

Among his former Golden Valley teammates, one said Tamura did take “a lot of head shots” because of his stature and playing running back. Another remembered him getting tackled at the line of scrimmage by players who outweighed him by 60-plus pounds. Only one recalled him sitting out because of injury. And that was for a broken arm.

“I don’t even remember him having any concussions or concussion-related injuries during our time together that had him out,” Castillo said.

Tamura transferred to Granada Hills Charter School for his senior season and rushed for 616 yards and five touchdowns. Tamura eventually received his GED in California, the source close to the family said, and never played in college.

Other than a video interview following a Granada Hills football game, Julian Torres, one of Tamura’s teammates at Golden Valley, said the next he heard about Tamura was years later.

“A few weeks ago when our friend had gone to Vegas,” Torres said. “And they just happened to see him working at, I guess, one of the casinos.”

In Nevada, Tamura appeared to work mostly in security and surveillance. Records provided by the Nevada Private Investigators Licensing Board show Tamura applied for a license, which was provisionally issued on Dec. 28, 2019, and worked for Securitas USA from February 2020 until December 2021. Registered as “unarmed,” the license expired Dec. 28, 2024.

Tamura worked for Securitas at the Lake Las Vegas resort in March 2020, when the Henderson (Nev.) Police Department listed him as a witness, assisting officers when two people were arrested for trespassing.

Months later, Tamura worked the overnight shift for Securitas in the Lake Las Vegas area when he told police he observed 75 gallons of fuel being stolen and alerted police — including logging the license plate of the vehicle stealing the fuel, according to police records.

On Wednesday, at the Securitas office in Henderson, an employee declined to comment about Tamura. There was no reply to an email from ESPN detailing questions about Tamura’s employment there.

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Early on the morning of Sept. 27, 2023, Tamura was gambling inside the red-carpet-shaded casino at the Red Rock Resort when security approached to see his identification. Tamura refused, which led security to ask him to leave.

Tamura tried to collect his winnings — almost $5,000 — at one of the nine cashier clerk stations. Casinos typically ask to see ID with larger payments. Tamura refused, according to a police report. Security then asked police to get involved.

Las Vegas police determined Tamura was “agitated,” according to the report, and that he “reached out” toward a security guard. Police forced Tamura toward a wall. When he didn’t cooperate, he was handcuffed and placed in a holding cell, where he refused to give his name and birthday.

Threatened with arrest, Tamura eventually did and was escorted out of the casino and told he was trespassing. Tamura was taken out of handcuffs and told he could leave. Instead, the report said, he threw his ID on a patrol car hood and leaned on it, refusing to leave and asking about his money.

He continued to remain on Red Rock property and was arrested for “Trespass After Verbal Warning,” according to records. Two months later, prosecutors decided not to charge him, and the source close to the family said Tamura eventually received his money. A Red Rock spokesman declined to comment.

According to the source, about two years ago, Tamura landed a surveillance job at the Las Vegas Strip’s Horseshoe Casino, which features multiple pits of table games at the casino’s center in front of the cashier’s station and a World Series of Poker Hall of Fame room.

One Nevada casino surveillance employee, who did not work with Tamura at the Horseshoe or otherwise know him, said casino surveillance work can be isolating. Employees are in many ways separate from the rest of the casino. Since they are tasked with rooting out cheating, they usually work in rooms away from both the casino’s patrons and its employees. They are not allowed to share meals with fellow employees for fear of fraternization.

“You can’t be seen, you can’t be heard, you can’t interact with others,” the employee said. “If they’re doing some sort of giveaway or contest, you can’t participate in it. So it does have, I would say, a negative effect on a person’s mental health.”

The source close to the family said Rick Ackley, a longtime surveillance worker in Las Vegas, hired Tamura and was his supervisor.

Tamura often worked the overnight shift, the source said, and recently had mentioned applying for an earlier shift — for better hours, a step up in his career and potentially a way to better handle the headaches. He occupied locker drawer No. 11 at the Paris Las Vegas Hotel & Casino, next door to the Horseshoe, both hotels owned by Caesars Entertainment.

When law enforcement searched his locker two days after the shooting, they took nothing from it, according to the search warrant.

Ackley’s attorney told ESPN that on Oct. 2, 2024, his client sold Tamura the gun used in the shooting, while “lawfully complying with Nevada and Federal gun laws,” and that Ackley sold Tamura the BMW he drove, beginning July 26, from Las Vegas to New York.

Horseshoe Casino employees directed questions to the casino’s parent company, Caesars Entertainment. Messages to Caesars went unreturned, but a company spokesperson told ABC News on Tuesday that Tamura was an employee there.

La Jolla Classics is typically a quiet, unassuming subdivision just outside Las Vegas. Tamura’s parents moved there from California in 2021. Shane Tamura had not lived in the neighborhood with his parents, the source said. Instead, he lived in multiple places around Las Vegas before settling into Paradise Royale, an apartment complex blocks off the Strip.

Law enforcement spoke with Tamura’s family at their home following the shooting, the source said, but never executed a warrant or searched the family home. On Friday, Nevada courts unsealed two search warrants — for the Paris locker and Paradise apartment.

Investigators have said Tamura left two notes — one at the shooting scene in New York and the second in another Las Vegas apartment where he lived. He apologized multiple times — to his parents, to “Rick,” and wrote “study my brain please I’m sorry.”

One former teammate read reports about Tamura’s notes, which he said reminded him of the friend he once knew but with whom he had lost touch.

“The way it was written kind of read in his voice in my head, which made me really sad,” former teammate Tobenna Okunna said. “I just remember in his speech pattern, he would say sorry a lot at the end of sentences.”

After the deadliest mass shooting in New York City since 2000, KPMG, Blackstone and the NFL all closed their offices Tuesday. In a memo to employees, the NFL told those based in New York to plan to work remotely at least until the upcoming Friday and to not try to enter the building, as the office will remain closed during this time. The NFL memo also urged staffers to be there for each other and to seek additional support if needed.

ESPN investigative reporter Paula Lavigne contributed to this report.