The officer found the little girl strapped in her car seat in a parking lot after earlier finding the baby's father unconscious near the car.
According to Maryland police, the man was under the influence of drugs.
The officer found the baby hours later, when he came back to the scene.
He says at first the child wasn't moving, but luckily he started to see her chest rise and fall.
The baby was pulled from the car. She is now with her grandmother.
As for her father, he is now charged with reckless endangerment.