FREMONT (CBS SF) — A man was arrested for the violent sexual assault of a female victim at a 24 Hour Fitness gym in Fremont on Monday – which was stopped by a quick-acting Good Samaritan –  and detectives believe there may be other potential victims, police said.

Police identified the suspect as 33-year-old Jonathan Anderson, who they described as a transient. At around 6:20 p.m., police said the victim was doing push-ups while attending a workout class inside the 24 Hour Fitness in the 39300 block of Paseo Padre Parkway.

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Jonathan Anderson (Photo: Fremont PD)

Anderson entered the class without warning, approached the victim and pushed her to the ground, police said. Anderson, a large man standing at 6 feet, 1 inch tall and weighing 255 pounds, forced the victim to the ground, pulled down her clothing and attempted to sexually assault her.

The woman screamed for help and a Good Samaritan in the gym immediately came to her aid, pushing Anderson off of her and standing in between the two to stifle any further assault.

Gym employees then became aware of the situation and also stopped Anderson until police arrived and took him into custody.

Police interviewed several witnesses and gathered video evidence from the gym, but Anderson later confessed to the attack in detail.

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He was on active probation for two prior convictions – a DUI and a prior grand theft. He has remained in custody since his arrest.

Anderson will be charged with felony sexual assault, felony assault with intent to commit oral copulation and probation violation. His arraignment is scheduled for Feb. 20.

Detectives are seeking to speak with anyone who may have contacted Anderson recently due to the severity of his actions and the nature of the crime. They believe the assault on the woman in the gym may not have been the first time he assaulted someone in a similar manner.

Police also offered praise for the Good Samaritan’s actions in helping the victim.

“The Fremont Police Department wishes to thank the Good Samaritan for intervening in the attack,” said Lt. Michael Tegner.  “Their quick action stopped this horrendous assault and aided in the suspect’s quick arrest.  It took bravery and courage to intervene.”

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Anyone with information about this incident is asked to please call the Fremont Police Department’s Investigative Unit at 510-790-6954 or send an anonymous tip by texting TIP FREMONTPD followed by your message to 888-777, or via the web at