As RedState reported, there was a mass shooting incident in New York City on Monday night, where the gunman opened fire in the 345 Park Avenue building, killing four people, including off-duty NYPD officer Didarul Islam, who was working as a security guard.

Islam was a father of two, and his wife is 8 months pregnant with their third child.

The shooter, identified as 27-year-old Las Vegas casino security guard Shane Tamura, also injured others before taking his own life. Officials say he has a "documented mental health history."

On Tuesday, the NYPD shared excerpts of what appears to be a suicide note from Tamura, who was a former football player but not with the NFL:

Investigators on Tuesday were focusing on whether a gunman had been targeting the headquarters of the National Football League when he burst into an office tower in Midtown Manhattan and killed four people, including a police officer, in a rare episode of deadly mass violence in the city.

Mayor Eric Adams said on Tuesday morning that the authorities “have reason to believe that he was focused on the N.F.L.,” which has offices at the tower, 345 Park Avenue. A three-page note found on the gunman mentioned the league, as well as claims that the man had suffered from the degenerative brain disease chronic traumatic encephalopathy, or C.T.E., from playing football, the police said. It asks that his brain be examined for signs of C.T.E. and accuses the league of concealing the dangers of the game.

Here's more from the NYT:

The note made reference to former N.F.L. player Terry Long and drinking “a gallon of antifreeze” — the method by which Mr. Long killed himself in 2005.

Mr. Tamura shot himself in the chest, rather than the head.

“Study my brain please,” the note said. “I’m sorry.”

The second of the four murder victims has also been identified:

Blackstone said in a statement to USA TODAY that Wesley LePatner, a senior managing director, was killed in the shooting.

"We are heartbroken to share that our colleague, Wesley LePatner, was among those who lost their lives in the tragic incident at 345 Park Avenue," the statement said. "Words cannot express the devastation we feel. Wesley was a beloved member of the Blackstone family and will be sorely missed."

This is a developing story. We'll keep you posted on updates.