Officers responded to the burger joint near 33rd Avenue and Indian School Road at about 2 p.m. Sunday and found the child inside the bathroom, KFAR reported.
The baby was pronounced dead at the scene, cops said.
Police released surveillance footage showing a person of interest, a woman who is seen wearing a black Calvin Klein shirt, black pants and sandals.
She tries to open a door and then walks back through the dining area before moving out of sight of the camera.
Police Sgt. Philip Krynsky told KOLD that detectives are investigating the shocking case, adding that no one has been arrested so far.
The autopsy results are pending, police said.
Police believe there are witnesses who left the eatery before police got there.
Anyone with information is asked to call Silent Witness at 480-WITNESS or 480-TESTIGO for Spanish speakers.
There have been several recent incidents of newborn babies being abandoned in public.