ROCKS shattered a moving car's sunroof on the M7 at Rooty Hill last Saturday.
The rocks were apparently thrown from the Eastern Road overpass, striking a black BMW sedan travelling south at about 11.25am.
The driver, a 42-year-old woman, was not hurt, despite the sunroof breaking and covering her with glass fragments.
She stopped on the side of the motorway and contacted police.
Investigators photographed the vehicle and towed it away because of the large amounts of broken glass within.
Police are appealing for anyone who witnessed the attack to contact Mount Druitt detectives on 9625 0000 or Crime Stoppers on 1800 333 000.