The fiend behind Sunday’s bloodbath at a packed Austin bar was an ex-New York City resident wearing a “Property of Allah’’ hoodie — and possibly out for vengeance over the US attack on Iran, law-enforcement sources told The Post.

Crazed Texas shooter Ndiaga Diagne, 53, of Senegal arrived in the US on March 13, 2000 on a B-2 tourist visa during the Democratic Clinton administration and became a lawful permanent resident (IR-6) when he married a US citizen in June 2006, a source familiar with his immigration history told The Post.

He then became a naturalized US citizen on April 5, 2013 around the start of former President Barack Obama’s second term — despite his growing rap sheet spanning New York and Texas.

On Sunday, the killer had a Quran in his car and was possibly also wearing an undershirt featuring the Iranian flag or other Iranian symbols when he opened fire on Buford’s Backyard Beer Garden near the University of Texas-Austin campus, according to sources familiar with the investigation.

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Law enforcement knew him as an emotionally disturbed person in both New York and Texas before Sunday’s bloody rampage, sources said.

He also had a string of previous arrests under his belt in the Big Apple and Texas, sources said, including a 2022 arrest in the Lone Star State for collision with vehicle damage.

In New York City, he notched busts between 2001 and 2016, the year he applied for asylum under the waning Obama administration.

Diagne was arrested in 2001 for illegal vending. His other three city arrests are sealed, sources said. Details on his Texas busts were not immediately known.

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“Obviously it’s still way too early in the process to determine the exact motivation but there were indicators on the subject and in his vehicle that indicate potential nexus to terrorism,” said Alex Doran, acting Special Agent in charge of the FBI’s San Antonio office, to reporters.

The attack happened about 2 a.m. — closing time for the popular nightspot — as hundreds of people were leaving to head home.

Diagne’s large SUV was spotted traveling around the block several times before he stopped in front of the bar and began shooting out of his front window with a pistol, hitting patrons on the front patio, according to Austin Police Chief Lisa Davis.

He then parked his car, got out and began shooting at people walking by on the street, the chief said.

Police confronted the shooter within less than a minute of the first gunshot at an intersection on 6th Street and shot him, cops said.

Two victims and the shooter died at the scene. First responders rushed 14 other patients to nearby hospitals, three of whom were in critical condition.

“Our hearts go out to the people that are victims of this and I want to reiterate my thanks to our public safety officers and officials that so rapidly were on the scene, they definitely saved lives,” Austin Mayor Kirk Watson said.

“This act of violence will not define us, nor will it shake the resolve of Texans. To anyone who thinks about using the current conflict in the Middle East to threaten Texans or our critical infrastructure, understand this clearly: Texas will respond with decisive and overwhelming force to protect our state,” Texas Gov. Greg Abbott said in a statement.