Authorities believe 67-year-old Joseph Lewin, of Port Chester, abused at least five kids.
The alleged abuse took place between 2001 and 2014 at two gyms once owned by Lewin.
The investigation began after one victim came forward, and the investigation led investigators to believe Lewin abused at least four other youngsters.
"We're concerned there could be more victims," Dectective Lieutenant Michael Colbath said.
In addition to the facilities he owned, police say Lewin -- who has also gone by the name Joseph Lewandoski -- worked at several gyms and camps throughout Rockland.
Investigators are encouraging other, now possibly adult victims, to contact police.
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