The man accused of gunning down three people at a Bronx apartment building was a disgruntled tenant who lost his temper during an ongoing dispute with neighbors over their shared backyard, according to law enforcement sources.

Jimmy Avila, 44, was arrested Wednesday after blasting away at three men around 8:30 a.m. on College Avenue near East 170th Street in Mount Eden — striking a 37-year-old in the chest, hitting a 59-year-old in the buttocks and shooting a 62-year-old in the arm.

The 37-year-old later died of his injuries, but the other two were hospitalized in stable condition.

Avila barricaded himself inside an apartment — and called a local news station and confessed — before he was eventually arrested after a stand-off with police.

The violence broke out during an argument over access to the building’s backyard, which Avila reportedly believed was his alone because he lived nearby on the first floor, the Daily News reported.

“I didn’t mean to do this, but I had to do it because these people were threatening my life,” he told News 12 in the frantic phone call while he was hiding.

His victim — identified by the Daily News as Ryan Hines — was the building’s superintendent who was gunned down as he walked by Avila’s apartment that morning.

The tenant struck in the arm — Orlando Nieves — was walking with the Hines when the gunfire erupted.

“My husband got hit twice,” his wife, Ebony, told the outlet. “He was ducking down, and I was pulling him through the door.”

“We’ve had problems with him for over a year,” she added. “He has the issue where anybody going in the backyard, he feels like it’s his and nobody else in the building can go back there.”

Avila has three convictions on his record, including a 2024 misdemeanor assault, and charges for possession of a controlled substance and burglary-related charges from the late 1990s.