The incident occurred around 4 a.m. May 16 at a 24 Hour Fitness on Sunnyvale-Saratoga Road, according to the Sunnyvale Department of Public Safety.
Authorities said the case appears to be an isolated incident and officers were at the gym Monday gathering witness statements and reviewing security camera footage.
Gym-goers expressed shock and concern over the reported invasion of privacy.
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"Absolutely surprising - shocking. I've never even felt uncomfortable," one person said.
"I find it super creepy, I come into this gym all the time. So, it's just weird that somebody would come early in the morning and do such a thing, in such a nice area," Sneha Shukla said.
The department has released limited information as the investigation remains in its early stages. Officials have not publicly identified a suspect but confirmed efforts are ongoing to locate the individual involved.
We did speak with the gym's general manager, who says staff is aware of this incident and is working with police. But as far as media requests, those go through corporate. At the time this story aired, we have yet to hear back.
Jenna Burkhalter, a regular at the gym, said the incident is troubling but has not changed her sense of safety during early-morning workouts.
"It is disappointing to hear that people's privacy is being infringed on like that," she said.
Other members said additional security measures could help prevent similar incidents.
"People walking around on the floor, I think would be good - that are part of the team," fitness coach Brandon Lacayo said. "I think that's something that we're lacking here at 24 Hour Fitness and in general across a lot of gyms. Staff don't really walk around the floors that much, ensuring that everyone is safe and that nothing, like that, is happening, right?"
Anyone with information about the case is urged to contact the Sunnyvale Department of Public Safety.