Investigators were being frustrated Tuesday by uncooperative witnesses in a wild Brooklyn shooting the night of July Fourth in which seven people were wounded amid a night of widespread violence across New York City, officials said.

The shootings at 410 Chauncey St. in the Ocean Hill section may have been sparked by a shooter being denied access to a party, police said. Four men and three women were wounded and police said there may have been more than one gunman, according to a law enforcement source who didn’t want to be named.

Police said they were questioning a person of interest in the shootings but had not made any arrests.

The shootings were among 12 incidents in the city on July Fourth in which 20 people were injured. Last year, six shootings with six victims were reported, NYPD records show.

As of 6 a.m. Tuesday, the early morning after the holiday weekend, police had recorded two shootings with two victims, half of what the city had in the same period last year, police said.

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The bloody holiday came at a time when the city has experienced a significant drop in shootings this year. Through July 3, the city had experienced 445 shootings, compared with 555 in the same period for 2015, a drop of 19.8 percent. There have been 529 shooting victims so far this year, down from 649 in 2015, a drop of 18.5 percent, police data showed.

In recent comments, James O’Neill, NYPD chief of department, has attributed the marked drop in shootings to a series of gang offensives this year which have targeted violent crews, especially in parts of Brooklyn and Manhattan. Last week, officials announced a large takedown of reputed members of two gangs in upper Manhattan whose street battles are believed to have precipitated the shooting which took the life last October of Detective Randolph Holder.

But police also have faced numerous cases in which those who are victims of shootings have not cooperated with investigators, something NYPD Commissioner William Bratton has noted several times.

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While the shooting on Chauncey Street was the most bloody, there were episodes of gunfire in Manhattan, Queens, the Bronx and Staten Island, police said.

Until July Fourth, the 73rd Precinct, within which Chauncey Street is located, had experienced a 23 percent drop in shootings so far this year, better than the citywide average.