“When I look into you and dad’s eyes, I see complete disappointment,” the letter stated. Tamura grew up in Santa Clarita, near Los Angeles, where his father served 18 years with the LAPD. Records show he acquired a security guard license from the California Bureau of Security and Investigative Services on March 7, 2019, which was valid until March 31, 2021.

In Nevada, he also held a private investigator license listing his parents’ address as his own, issued in December 2019 and expired on December 28. Despite being noted for not legally carrying a firearm due to a ‘no’ firearm status and a documented mental health background, as explained by New York City Police Commissioner Jessica Tisch, Tamura managed to secure a concealed firearms permit from the Las Vegas Metropolitan Police Department. He had this permit when he entered the skyscraper at 345 Park Avenue, Midtown Manhattan, resulting in four fatalities.

After making a cross-country trip for his daylight attack, Tamura, who was last employed at the Horseshoe Las Vegas hotel and casino’s surveillance department, seemed to attribute his mental health struggles to the NFL.

On his body, a three-page note was discovered criticizing the NFL’s response to chronic traumatic encephalopathy (CTE), linked to sports with head trauma. “Terry Long football gave me CTE and it caused me to drink a gallon of antifreeze,” he wrote per CNN. “You can’t go against the NFL, they’ll squash you.”

Tamura referenced Terry Long, a former Pittsburgh Steeler who ended his life in 2006 after battling CTE. His note pleaded for a brain study and apologized repeatedly. Police also uncovered medication inside the BMW he drove across the country.

When he finally reached the lobby of the high-rise office building, where the NFL is headquartered, at around 6.30pm on Monday, Tamura opened fire – shooting NYPD Officer Didarul Islam (pictured) in the back and a security guard who took cover behind a desk.

He then proceeded up to the 33rd floor, the offices of Rudin Management – which runs the building and other offices across the Big Apple – where he shot and killed Rudin employee Julia Hyman (pictured). Blackstone executive Wesley LePatner and security guard Aland Etienne were also killed in the attack. Police now believe was the shooting was premeditated and likely [self-murder].

‘It appears that he knew it would be his last stand,’ said CNN chief law enforcement analyst John Miller, a former NYPD deputy commissioner. ‘He fully intended to shoot his way through the lobby and make his way to that target – whatever that might have been.’ It has since been revealed that an associate also sold him gun parts for the M4 assault rifle he used in the attack. In a video update on Tuesday, Tisch said investigators were heading to Tamura’s Las Vegas home to conduct interviews and execute a search warrant. ‘The weapon used, an AR-15-style assault rifle, was assembled by Mr. Tamura using a lower receiver purchased by an associate. We have located that associate and others. And will be questioning him about that purchase,’ she said.

Meanwhile, Tamura’s old high school friends said they were stunned to learn the former running back was the mass shooter. ‘You never would have thought violence was something you’d associate with him,’ classmate Caleb Clarke told NBC. ‘Everything he said was a joke.’ His former coach Walter Roby also said Tamura was a talented football player and a ‘quiet kid’. ‘I’m just blown away right now,’ he said.