Gunman who killed four left note with one request before opening fire in New York building

A gunman who opened fire in a skyscraper in New York City and killed four people left a note that laid out a specific request, according to sources.

The suspected gunman, who was identified by police as Shane Tamura from Las Vegas, US, entered a high rise building in Park Avenue, Manhattan on Monday evening (28 July) and began firing a rifle.

Police have confirmed that, as well as the four casualties including a police officer, a fifth man was also shot and is currently in a 'critical but stable condition'.

After his killing spree across several floors of the building, Tamura then shot himself in the chest.

Earlier today, Police Commissioner Jessica Tisch said the gunman had a ‘documented mental health history,’ but authorities were trying to work out a motive, including why he targeted that particular location.

And now, The New York Post says that Tamura had left a note behind which may have hinted at a possible motive.

The man who opened fire in a skyscraper in Manhattan reportedly left behind a 'suicide note' (NYPD)

In the alleged note, which was reportedly several pages long, Tamura supposedly blamed football for his struggle with a neurodegenerative disease called chronic traumatic encephalopathy (CTE), law enforcement sources said.

According to the NHS, Chronic traumatic encephalopathy (CTE) is a brain condition thought to be linked to repeated head injuries and blows to the head.

The condition slowly gets worse over time and leads to dementia, but the symptoms can be managed. In his alleged note, he reportedly also asked that his brain be studied after his death.

Tamura was reportedly a security guard at a Las Vegas casino, but in high school, he was a ‘standout football player’, The New York Post claims.

The office also houses the NFL headquarters, with NFL Commissoner Roger Goodell revealing that one of the employees had been 'seriously injured in this attack' and was 'currently in the hospital and in stable condition'.

According to NBC News, officials are looking into a note from the suspect, however, a motive has not yet officially been determined.

The note comes as police are trying to work out a motive for the horrific attack (Liao Pan/China News Service/VCG via Getty Images)

They also added that the investigation is currently ongoing.

Surveillance footage showed the shooter exiting a car just before 6.30pm carrying an M4 rifle, before he then entered the building.

The officer killed in the attack was Didarul Islam, 36, an immigrant from Bangladesh who had served as a police officer in New York City for three and a half years.

“He was doing the job that we asked him to do. He put himself in harm’s way. He made the ultimate sacrifice,” Commissioner Tisch said. “He died as he lived. A hero.”

The other victims are yet to be named.