Police say Kyle Williams was one of two people who opened fire during the gathering in Brooklyn in July.

New York City police have arrested a 20-year-old man in connection with a mass shooting over the summer at a Brooklyn community festival that left one person dead and 11 wounded.

Police said the gunman, Kyle Williams, was one of two people who opened fire – possibly shooting at each other – during the Old Timers Day gathering in the Brownsville section of Brooklyn on July 27.

The gunfire sent a crowd of thousands of people, who had gathered in the area around a playground and community centre for music and food, scattering. Flying bullets cut down partygoers as they fled the event, held annually as a reunion for people who grew up in the neighbourhood.

One person, Jason Pagan, 38, was fatally struck by gunfire. Police said earlier in the investigation that Pagan had recently been let out of prison and the shooting might have been related to a gang dispute.

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Pagan was a member of the Bloods gang and several other victims had gang histories, police said.

Williams was arrested late on Wednesday on charges of murder, criminal possession of a weapon, reckless endangerment and attempted murder charges. He was expected to be arraigned Thursday, the Brooklyn District Attorney’s office said. It was not clear if he had a lawyer who could comment.

Police did not immediately say how they were able to identify Williams as one of the gunmen. The address police listed for him is about a 10-minute walk from the playground.

Attempt to drive down crime

The investigation had, for a time, seemed stalled.

Police offered thousands of dollars in rewards for information. In recent weeks, the department publicised the pictures of two women and asked the public to help identify them as part of the investigation.

The shoot-out left six men and five women ages 21 to 55 hospitalised with gunshot wounds.

Police Commissioner James O’Neill said 2,000 to 3,000 people attended the Old Timers Day event and that more than 100 police officers were stationed there on the night of the shooting in an attempt to prevent violence.

Brownsville, one of the poorest sections of Brooklyn, has seen crime plunge in recent years much like the rest of the city. But it still ranks as having more gun violence than most other places. O’Neill said gang violence accounts for about half the shootings in the area.

Brownsville’s police precinct is one of six in the city receiving special attention from the NYPD to drive down crime.

By some measures, it is working.

So far this year, there have been 11 killings in the precinct, according to police data – two fewer than at the same point last year. This year, there have been 28 shootings – eight fewer than at the same point last year.