A teacher's aide in Brooklyn was arrested Thursday for allegedly groping a 13-year-old girl at a public park, the NYPD said.

A witness observed Jesus Lorenzo, 69, inappropriately touching the girl at De Hostos Playground and called police. Lorenzo has been charged with endangering the welfare of a child, forcible touching and sexual conduct with a minor.

It's unknown how Lorenzo knew the girl, although she is a student at IS 318 in Williamsburg, where Lorenzo works. The victim reportedly has Down's Syndrome.