Upper Merion Township Police said on July 3 they were dispatched to the mall's Hollister store where a 14-year-old girl found a pen equipped with a tiny camera.
Police said she found the pen inside the store's dressing room after she had already tried on clothes.
The device was placed at waist level, in between the curtain and the divider.
"It's disgusting," said shopper Julie Rallis, from Wilmington, Delaware.
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"Considering I have a daughter, yeah I don't want that going on," said shopper David Graycar or Royersford.
Police have accused 26-year-old Joseph Stevenson of Smyrna, Delaware, of placing the camera in the dressing room.
Officers said they were able to track Stevenson down after he asked a store employee where his pen went.
Stevenson admitted to placing another camera pen inside an Urban Outfitters dressing room at the mall, police said.
An employee identified an identical pen while checking the store fitting rooms.
Police said two juvenile girls were filmed inside the dressing room between 2:20 and 2:55 p.m. Police are still trying to contact the two victims. All the victims from Hollister have been contacted.
"You know that those two stores usually cater to younger girls, teenage girls, so that's very scary," said Alyson Sciacca, who said she has a teenage daughter.
"Especially having a daughter trying on clothes here at the mall, it's something we come and do all the time, I'm very upset over that," said Stacey Reed from King of Prussia.
In total, Stevenson is accused of recording nine victims ranging from a 13-year-old girl to a 29-year-old woman.
The device records video and audio but because it has a USB drive, police do not think Stevenson had accessed the images.
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"It's very disturbing. I think anyone that goes into a changing room and pulls a curtain behind them expects to have privacy, and that privacy was invaded," said Tom Nolan, the police chief of Upper Merion.
Mothers like Stacey Reed shopping on Friday said they'll have a conversation with their children about being vigilant inside a mall dressing room.
Reed went as far as to say she and her pre-teen daughter won't be trying on clothes in any dressing rooms for now.
"That's a shocker, oh my goodness, wow. Doesn't make me feel comfortable trying on clothes any longer," said Reed.
"That's just frightening to think about, because that could have been myself and my friends. I definitely don't want that happening. That's pretty scary to think about," said Kyla Riley from King of Prussia.
Stevenson has been charged with invasion of privacy, interception, disclosure or use of wire communications, and disorderly conduct. Stevenson has been arraigned on the charges and has been 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.
Upper Merion Police said you should contact police, security or store management if you notice anything suspicious when you are at the mall.