A woman was killed in a point-blank shooting outside a Brooklyn deli that law enforcement sources said was carried out by an ex-girlfriend.

The execution-style killing took place on a sidewalk at the corner of St. Marks Place and 4th Avenue in Park Slope after 1 p.m., police said. A 51-year-old woman, later identified as Nichelle Thomas, was about to enter a local bodega when another woman could be seen on surveillance video walking up behind her, pulling out a gun and shooting her in the back of the head.

The shooter, dressed in all black, fled the scene. Thomas was rushed to the hospital, where she died. Workers at the bodega at the time of the shooting said the victim was a frequent customer and well-liked.

Police said that Latisha Bell was arrested after turning herself in at a stationhouse later Wednesday evening. The 38-year-old was charged with second-degree murder and criminal possession of a weapon. Attorney information for Bell was not immediately clear.

Neighbors said that Thomas, who lived just a couple blocks from where the shooting took place, and Bell had a volatile relationship, fighting often. It was not known how that escalated to the killing.

A police investigation is ongoing.