An unusual oxidation type on bulb filament after a car crash dive

A car with two dead bodies trapped inside was discovered in a gravel pit. The main hypothesis of investigators was a traffic accident simulation by night. Examination of a broken light-bulb revealed both a rather unusual oxidation type and small rounded cavities never reported before. Tests were performed and allowed forensic scientists to establish that the lightbulbs were switched on during the crash dive, in contrast with the investigators idea.