Three people were killed over the weekend in separate shootings in Manhattan, Brooklyn and the Bronx, including one right behind an NYPD precinct stationhouse in Harlem, police said.

NYPD officials announced no immediate arrests in any of the incidents.

Police said gunfire erupted around 11:45 p.m. Sunday behind the 28th Precinct stationhouse on Frederick Douglass Boulevard and West 123rd Street in Harlem and struck a man on the sidewalk in his head.

First responders took him to St. Luke’s Hospital, where he was pronounced dead, and officials had not publicly identified him by Monday morning. The NYPD said ballistic evidence was recovered at the scene but detectives were still investigating what sparked the shooting.

Flower seller Nicacio Lazaro Hernandez said on the corner Monday morning that shots rang out right in front of him as he was closing up his stall for the night.

“A man started following [the victim, who] pulled out a knife … and the other man pulled out a gun and shot,” he said. “I heard three shots.”

Lazaro Hernandez said he recognized the victim as a combative regular in the neighborhood. He added that he did not hear the man or two others who were apparently following him exchange any words.

Surveillance video from the deli on the corner shows two men crossing into the frame at the time of the incident. Then, a third man crosses into the frame, pulls out a gun and fires, according to the footage, which Gothamist reviewed.

Several hours earlier on Sunday, police in the Bronx responded to a 911 call around 6:45 p.m. about two people shot near East 188th Street and Marion Avenue in Fordham Heights, according to officials.

When officers arrived, they found 57-year-old Kevin Jennings shot in his head and a 34-year-old woman shot in her left leg. Paramedics took both victims to St. Barnabas Hospital, where Jennings was pronounced dead and the woman was in stable condition, police said. The NYPD did not have a description of a possible suspect or motive, but said Monday both Jennings and the woman were bystanders.

And just before 10 p.m. Saturday night, 18-year-old Zanir Childs was shot and killed on New Jersey and Hegeman avenues in East New York, across the street from P.S. 36, officials said. Police said Childs was struck in his torso and an 18-year-old woman was hit in her right arm.

Childs was pronounced dead at Kings County Hospital Center, while the woman was taken to Brookdale Hospital in stable condition. NYPD officials did not have details about a possible suspect or motive by Monday morning.

Through May 11, shootings were down more than 66% in the 28th Precinct, which covers Central Harlem, compared to the same period last year, police data shows. In April, 61-year-old Excenia Mette became the precinct’s first fatal shooting victim this year, after officials said she was struck and killed by a stray bullet while checking on her grandson several blocks north of Central Park. Police later arrested two 23-year-old men in connection with the shooting.

Shootings in the 46th Precinct, which includes Fordham Heights, dropped 17% through May 11, while homicides fell 90%, according to the NYPD. Jennings is the only person to die from gun violence in the precinct so far this year, according to Gothamist’s analysis of police data.

In the 75th Precinct, which includes East New York, two people were previously shot and killed this year, officials said. NYPD data shows the precinct recorded a 24% decrease in shootings through May 11 this year.

More information about shootings across New York City over the last several years can be found on Gothamist’s gun violence map, which shows patterns across specific blocks.

Charles Lane contributed reporting. This is a developing story based on preliminary information from police and has been updated with additional information.