*

Four victims shot dead, including New York police officer

*

Authorities find manifesto, notes on the shooter regarding

CTE

*

Carnage unfolds in skyscraper housing NFL, financial firms

*

Blackstone executive was among those killed

(Adds detail on suspect, building tenants, mayor's comments)

By Lananh Nguyen and Michelle Nichols

NEW YORK, July 29 (Reuters) - New York City homicide

detectives sought clues on Tuesday to what possessed a Las Vegas

man to drive cross-country and storm into a midtown Manhattan

office tower to open fire with a military rifle, killing four

people, including a policeman.

Gunman Shane Tamura, 27, brought the carnage to an end not

long after it began on Monday evening by fatally shooting

himself in the chest on the 33rd floor of the Park Avenue

skyscraper.

The building houses the NFL headquarters and offices of

private equity giant Blackstone, the accounting firm KPMG

and real estate company Rudin Management, among other major

financial firms.

Police said the shooter when he was found was carrying "a

manifesto" and notes about chronic traumatic encephalopathy

caused by head trauma, Bloomberg News reported, citing two

senior law enforcement officers.

He wrote that the NFL did not do enough to address CTE,

which has been linked to cognitive, emotional, and behavioral

problems in former players. The suspect had played football

before a head injury ended his career, Bloomberg reported.

"We're still investigating," New York City Mayor Eric

Adams told MSNBC's "Morning Joe" program in an interview on

Tuesday, adding that investigators have reason to believe the

shooter was focused on the NFL offices housed in the building.

Among the four victims slain was Didarul Islam, 36, a New

York Police Department officer who immigrated to the U.S. from

Bangladesh. Mayor Eric Adams described the officer, who had been

on the force for about three and a half years, as a "true blue"

hero.

A Blackstone executive was among those killed in the

shooting, the Wall Street Journal reported, citing people

familiar with the matter. Other employees of the investment

management firm are in the hospital receiving treatment, the

Journal reported.

An NFL employee was also injured in the shooting and was

in stable condition at a hospital, the Journal reported, citing

a memo sent by NFL commissioner Roger Goodell to league staff.

Goodell wrote there would be "increased security

presence" at the league's offices "in the days and weeks to

come," ESPN reported.

Authorities offered few details about the three other

victims - two men and a woman. A third man was gravely wounded

by the gunfire and was "fighting for his life" in a nearby

hospital, the mayor said.

HISTORY OF MENTAL ILLNESS

New York Police Commissioner Jessica Tisch told reporters

Monday night that the gunman appeared to have acted alone.

Tisch said Tamura had a documented history of mental

illness and appeared to have driven to New York from Las Vegas

over a period of three days.

According to recap of the shooting spree outlined by Tisch,

Tamura entered the skyscraper's lobby, turned to his right and

immediately opened fire on the NYPD officer, who was assigned to

the building's security detail.

The suspect then proceeded to shoot a woman and two men as

he sprayed the lobby area with gunfire but inexplicably allowed

another woman to pass him unharmed before he took the elevator

to the 33rd-floor offices of Rudin Management. There he fatally

shot his final victim before taking his own life, Tisch said.

A widely published photo of the shooter, that CNN said was

shared by police, showed him walking into the building carrying

his rifle. Preliminary checks of the suspect's background did

not show a significant criminal history, CNN reported, citing

officials.

Another widely circulated photo showed the permit issued to

Tamura by the Las Vegas Metropolitan Police Department allowing

him to legally carry a concealed firearm.

Tamura carried out his rampage, according to Tisch,

armed with an M4 carbine, an assault-style rifle used

extensively in the U.S. military.

A loaded revolver was later recovered from the black BMW

vehicle Tamura had left double-parked outside the office tower,

along with a backpack and prescription medications, she said.