An emotionally disturbed recidivist was arrested after he was spotted walking around a Bronx neighborhood with what appeared to be a long gun in broad daylight — less than 24 hours after a mass shooter killed an NYPD officer and three others at a luxury Park Avenue office tower.

The 42-year-old man — who has more than 70 prior arrests, including six gun charges — was nabbed shortly after police arrived at 1402 Nelson Ave. to canvass the Highbridge neighborhood around 12:30 p.m., according to the NYPD and law enforcement sources. 

A photo obtained by The Post shows the man wearing a black T-shirt, black shorts, white sneakers and a black backpack, toting the firearm in his left hand.

The armed suspect — known to police as an emotionally disturbed individual with multiple related arrests — allegedly told cops the gun he was carrying was an air rifle, law enforcement sources said.

The investigation is ongoing, with police working to execute a search warrant on the suspected perp. 

The latest scare comes just a day after gunman Shane Tamura, 27, stormed a posh Midtown skyscraper — home to Blackstone and NFL headquarters — and opened fire with a rifle around 6:30 p.m., killing four people before turning the gun on himself. 

Among the victims were NYPD Officer Didarul Islam, whose wife is pregnant with their third child; Blackstone executive and mother of two, Wesley LePatner; security guard Aland Etienna; and Julia Hyman, a management associate at building owner, Rudin Management.

The unhinged gunman, who journeyed from Nevada to unleash bloodshed in the Big Apple, left behind bizarre notes in his wallet claiming he had neurodegenerative disease chronic traumatic encephalopathy (CTE) — the brain disease linked to repeated blows to the head, commonly found in football players.  

Tamura’s scattered writing blamed football for his suspect case of CTE and begged for his brain to be studied in the wake of the massacre. 

“Please study brain for CTE,” he wrote in the three-page letter. 

“I’m sorry. The league knowingly concealed the dangers to our brains to maximize profits. They failed us.”

He also name-checked Terry Long, the former Pittsburgh Steelers player who was diagnosed with CTE after downing antifreeze to kill himself 20 years ago.

Mayor Eric Adams confirmed Tuesday that the mentally ill shooter appeared to have been targeting NFL’s corporate headquarters, which has offices in the 44-story building.

Investigators are still probing an exact motive for the bloodshed.