NEW YORK (CBSNewYork) — A man has died four days after being shot in Greenpoint, allegedly by his retired NYPD officer neighbor.

Joseph Stepinski, 45, was pronounced dead Friday at NYC Health + Hospitals/Bellevue, police said.

Retired NYPD Officer Gene Barrett, 51, already stood charged as of Tuesday with first degree attempted murder, first degree assault, first degree robbery, menacing, and burglary in connection with the shooting.

Charges are expected to be upgraded, police said.

Police say around 2:30 p.m. Monday, Barrett shot Stepinski outside of 185 Greenpoint Ave., where both men lived.

Witnesses watched it all unfold as Stepinski was shot at point blank range, once in the head, investigators said. Barrett then went through Stepinski’s pockets and went inside, police alleged.

Sources say when responding officers got to the scene, they saw Barrett through a first floor window with a gun and he said “it was me, it was me.”

“He pointed the gun at the officer,” a witness named Colleen said. “At that point, she kind a like backed up in the doorway of that building.”

After about an hour long standoff, he surrendered. Inside the home, police found two guns and two cell phones on the table.

Sources say Barrett had an ongoing dispute with Stepinski over Barrett’s rent stabilized apartment, CBS2’s Janelle Burrell reported. The victim’s girlfriend is apparently the building’s manager.

The landlord told investigators Barrett has lived in the building for about 25 years and had been a problem tenant. Barrett had several complaints filed against him, including complaints about bedbugs and being combative against other tenants.

Barrett — who retired from the NYPD in 2002 — has filed 12 complaints with police, eight of which involved the victim.

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