The shooting happened Friday at the Mill Creek rec center on the 4700 block of Brown Street around 1:30 p.m.
Police said Tiffany Fletcher, 41, was caught in the crossfire of a nearby gun battle.
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She was rushed to the hospital and placed in critical condition, but died just after 7 p.m.
During a news conference Monday, officials said police officers were in the area at the time of the shooting and ran toward the gunfire.
Police arrested a 14-year-old boy in connection with the deadly shooting. He is now charged with murder, officials said.
They also found a ghost gun in the trash, which they believe he ditched right after the shooting.
During the news conference, officials said they believe shots from the ghost gun are what killed the woman.
Fletcher, a mother who leaves behind three boys, just started working at the rec center this summer and was beloved in the community.
Police are now searching for two to three other suspects in the gun battle.
Anyone with information about the shooting is asked to call police.