BURBANK (CBSLA.com) —Autopsy results were “inconclusive” Tuesday in the death of a teenage boxer who died July 26 following a workout at a Burbank gym.

The L.A. County Coroner’s Office said it needs to do more tests to figure out what killed 16-year-old Raul Alvarez.

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Witnesses said Alvarez was sparring with someone about his same size and age at Pullman’s Gym, which is located at 4320 West Magnolia Boulevard.

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He was wearing protective gear.

Alvarez got dizzy and medics rushed him to the hospital, but he died about an hour later.

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“While at the hospital, the male suddenly went unconscious. All efforts by medical personnel to revive the male were unsuccessful and he was pronounced dead at the hospital about an hour later,” Sgt. Darin Ryburn of the Burbank Police Department said.