Upper Merion officers were dispatched on July 3 to the mall's Hollister store where a 14-year-old girl found the suspicious pen after she had already tried on clothes, 6abc reports.
The girl turned the pen over to store management who then contacted Upper Merion police, authorities said.
Officers identified Joseph Stevenson, 26, of Smyrna, Delaware as the culprit after he asked a store employee where his pen went, police told 6abc.
Stevenson then admitted to officers that he had placed an additional pen in the Urban Outfitters dressing room, police said. Store management found an identical pen while checking the dressing rooms.
The camera in the Hollister dressing room captured six women and one man, police said. They were taped in various stages of undress while trying on clothes.
All seven of the victims were identified and made aware of the investigation, authorities said.
Police are still looking to identify two juvenile girls who were filmed inside the Urban Outfitters dressing room between 2:20 and 2:55 p.m., police said.
Police said they have no reason to believe that Stevenson accessed the recordings because the pens have a USB drive.
The nine victims range in age from a 13-year-old girl to a 29-year-old woman, police told 6abc.
Stevenson has been charged with invasion of privacy, interception, disclosure or use of wire communications, and disorderly conduct.
He was arraigned on those charges and released on $10,000 bail.
Further conditions require Stevenson to have no contact with the victims or their families and to refrain from visiting shopping malls.
The department urges all individuals to contact police, security, or store management if they notice anything suspicious when they are at the mall.
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