The argument happened around 8 p.m. inside of an L.A. Fitness at 18400 Convention Center Dr. in Tinley Park, police said. The altercation then moved to the parking lot.
The offender, a Richton Park man whose identity was not known, retrieved a gun from his car and shot a man five times, police said.
The victim was taken to a hospital, initially in critical condition, police said.
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The offender was arrested and charges are pending as police continue to investigate.
No further information was immediately available.