Snapchat gender filter arrest.jpg

A California college student uses a Snapchat filter to take down a cop, allegedly looking to hook up on tinder.

Ethan is a 20-year-old student in the south Bay Area.

He told police he had a female friend who had been molested as a child, and went online to create an undercover profile to identify possible pedophiles.

The student -- who did not give his last name because he fears retaliation -- used Snapchat's gender-switch filter to take a picture of himself, then posed as a woman named "Esther" on Tinder.

According to Ethan, a man reached out to him -- asking, quote: "Are you down to have some fun tonight?"

Ethan then texted the man on a different app, saying that he was 16 years old.

Ethan said it didn't appear to matter to the suspect, because they began exchanging explicit messages for more than 12 hours.

"On purpose, I would just get these little bits of information from him, so I could, it would be easier to track him down -- for the police to track him down," Ethan said.

Ethan took several screenshots of their conversation and sent them to "Crime Stoppers."

Snapchat gender filter arrest.jpg
Snapchat gender filter arrest.jpg

That led investigators to a San Mateo police officer, named Robert Davies.

"I was just looking for someone, he just happened to be a cop," Ethan said.

He was arrested last week on suspicion of discussing sexual activity with a minor on social media.

Ethan said this is the first time he's done something like this, and doesn't intend to do it again.

Davies has been placed on administrative leave and is facing a charge of contacting a minor to commit a felony.

The San Mateo Police Chief released a statement about the arrest last week:

"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."