Investigators say Miles Lacy attempted to pull over a car being driven by an off-duty Houston police officer.
The officer and his family were on the Katy freeway in January when a BMW pulled behind them and turned on red and blue emergency lights.
The officer was pretty sure no local police departments were using luxury cars to catch speeders, so he took down the license plate number, and that led to an arrest.
Lacy, 22, has been charged with impersonating a public servant.
He posted $5,000 bond and was released from jail.