A retired NYPD officer allegedly shot his neighbor in Greenpoint yesterday, prompting a standoff with cops until he was eventually taken into custody. His victim is on life-support at Bellevue Hospital.

Gene Barrett, 51, allegedly shot neighbor Joe Stepinski, 45, on the sidewalk outside 185 Greenpoint Avenue (between Manhattan Avenue and McGuinness), where both Stepinski and Barrett lived, at around 2:30 p.m. yesterday. Barrett shot Stepinski, who was incorrectly identified as Barrett's landlord in earlier reports, in the head before taking his cellphone and keys, according to police, then allegedly barricaded himself inside the building. Cops locked down the building and persuaded Barrett to surrender around 4 p.m.

The Daily News reports that Stepinski's girlfriend, Melissa Rotundo, is Barrett's landlord. Barrett's motive for shooting Stepinski remains unclear, though a friend of Barrett's told NBC New York that Stepinski would "stalk him, spy on him, walk into his apartment. These are things he'd complain about."

A neighbor told the News that Barrett, who retired from the NYPD on a disability pension in 2002, "was always moody. He had real anger issues." The NYPD recovered two guns at the scene of yesterday's shooting.

Barrett currently faces an attempted murder charge.