A college student wanted to take down potential predators on Tinder. So, he posed as a teen girl using Snapchat's new gender-swap filter — and ended up catching a cop allegedly looking to hook up with a minor.

"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," San Mateo Police Chief Susan Manheimer said in a statement. "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.'

A Message to our Community Earlier today, a San Mateo Police officer was arrested by the San Jose Police Department for alleged crimes that occurred while he was off-duty in another county. As soon...