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SAN MATEO, Calif. – Snapchat’s gender-swapping filter has been used to make a viral Evanescence videoalter famous works of art, and reveal Glenn Close’s unexpected male celebrity look-alike since it launched in May.

Now, a use that’s a little more impactful: NBC Bay Area reports a local college student used it to create a female photo of himself, then used that image on a series of apps to ultimately expose a San Mateo cop who was allegedly willing to hook up with a minor.

Ethan, who opted not to provide his last name during his sit-down interview with the station, was rattled after learning a female friend of his had been molested as a child. So he decided to attempt a one-man sting to take down a pedophile.

The 20-year-old took a photo using the filter, and the Washington Post explains the benefit to doing so versus just lifting a picture from the internet: It made the photo seem more authentic: “Creating a unique image with the app meant that photo couldn’t easily be traced back to its rightful owner with a simple Google image search.”

Ethan used the photo to pretend he was an underage girl named Esther and created an online profile on Tinder. The man who allegedly responded was a San Mateo police officer named Robert Davies.

Ethan took screengrabs of their conversations, during which he said he was 16 years old. He told NBC Bay Area the chat started with Davies asking, “Are you down to have some fun tonight” and then the two switched to a different app and the messages became “a lot more explicit.”

“I was just looking to get someone,” Ethan told the station. “He just happened to be a cop.”

After Ethan turned over the evidence to authorities, San Jose police arrested Davies, who faces a possible count of contacting a minor to commit a felony. San Mateo police said Davies is on administrative leave and issued a statement calling the officer’s alleged actions “disturbing.”

San Mateo Police Chief Susan Manheimer said in a statement:

“This alleged conduct, if true, is in no way a reflection of all that we stand for as a Department, and is an affront to the tenets of our department and our profession as a whole. As San Mateo police officers, we have sworn an oath to serve and protect our communities. I can assure you that we remain steadfast to this commitment to serving our community with Professionalism, Integrity, and Excellence.”

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