The shooting was reported around 1:55 a.m. Thursday at the 24 Hour Fitness gym on Lone Tree Way, where Brentwood police said a fight broke out on or around the gym's basketball court and continued to its parking lot, where at least two people opened fire, based on surveillance footage.
Arana was pronounced dead at the scene, while the three others went to hospitals.
Police said later Thursday that two people had been detained in connection with the shooting, but no arrests had been made.
Anyone with information about the case is asked to call Detective Greene at (925) 809-7797.
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