On the 2oth of july1929 an accountant bought a newspaper and saw yesterday report which puzzled him a legendary pilot hero from World War 1 dies in a car crash under mysterious circumstances?

Actually, since it was 1929, it would not have been called the "first world war", since the second world war had not occured yet.

I searched for a WW1 pilot who died in a car crash. Here is a Canadian pilot.
ANDREW EDWARD McKEEVER, 1895-1919
A World War 1 flying 'ace', McKeever was born and raised in Elma Township. He enlisted with the Canadian Expeditionary Force in 1916 but, attracted by the life of the fighter pilot, transferred to Britain's Royal Flying Corps once he was overseas. From May 1917 to January 1918 McKeever was posted to the 11th Squadron on the Western Front. An outstanding operator of the two-seater Bristol Fighter, he, with his various observers or gunners, shot down some 30 enemy aircraft during reconnaissance missions and offensive patrols, earning the Military Cross and Bar and the Distinguished Service Order for his "conspicuous gallantry and devotion to duty". At the end of the war, McKeever returned home where, shortly afterward, he died as the result of a car accident.