NYC shooting: Police question man who supplied gun parts to shooter 

Editor’s Note: This article contains discussions of suicide. Reader discretion is advised. If you or someone you know is struggling with thoughts of suicide, you can find resources in your area on the National Crisis Line website or by calling 988.

(NewsNation) — Police are questioning an associate who helped a gunman obtain rifle parts used in a shooting Monday in New York City that left four people dead, including a police officer, authorities said.

The gunman assembled an AR-15 style rifle "using a lower receiver purchased by the associate," NYPD Commissioner Jessica Tisch said. Investigators have located and are questioning the individual about the purchase.

Shane Devon Tamura, 27, drove from Las Vegas to New York City and opened fire in a Manhattan high-rise building before killing himself. The shooting claimed the lives of NYPD Officer Didarul Islam and three others.

Tamura had a history of mental illness and played high school football in Southern California. His three-page suicide note referenced CTE and contained what officials described as "CTE facts."

Deputy Mayor for Public Safety Kaz Daughtry told NewsNation detectives have been sent to Las Vegas to assist with search warrants and interviews. The investigation involves the NYPD, Las Vegas police and federal partners.

Tisch said that two groups of detectives are on their way to Las Vegas to conduct interviews and execute a search at Tamura’s home.

The officers will also visit the gun store where he legally purchased a revolver on June 12 using a Nevada concealed carry permit, she said.

The slain officer leaves behind a wife who is eight months pregnant and two young children. The officer's father was hospitalized after learning of his son's death, telling the mayor through a translator, "He's my only son."

NYC gunman blamed the NFL, wanted brain studied

Mayor Eric Adams said Tamura left a suicide note claiming he had chronic traumatic encephalopathy, a brain disease linked to head injuries from contact sports. The gunman blamed the NFL and intended to target the league's headquarters in the building.

"The note was found on the suspect, he stated he had CTE, a brain injury known for those who played contact sports of some nature. And he seemed to have blamed the NFL," Adams said. "The NFL headquarters was located in the building. And he mistakenly went up the wrong elevator banks."

The mayor said Tamura shot himself in the chest, apparently to preserve his brain for research. The city's medical examiner will examine the gunman's brain as part of the autopsy.

How did the shooting unfold?

Security cameras captured Tamura stepping out of a black BMW and walking into the high-rise building carrying an AR-15 style rifle. He shot and killed the police officer and two other people in the lobby before taking an elevator.

A woman stepped off the elevator as Tamura was getting on, and he allowed her to walk away. He then went to the 33rd floor, home of Rudin Management, where he killed another person before taking his own life.

NewsNation's Steph Whiteside, Patrick Djordjevic and Brittney Donovan contributed to this report.