The body of Michael Bassett, 24, was found in a maroon Ford Escort (pictured) by two friends in a beauty spot near the village of Barlaston the previous evening.
There was a pipe from the exhaust into the car and Bassett was cradling a gun with a confession written on a local newspaper beside him.
He admitted shooting dead Monique Liebert 22, her sister Claudine Liebert, 20 - both teachers from Fontenay le Comte in northern France - and Claudine's fiance Daniel Berland, 20, a student from St Medard des Pres near Fountenay.
His letter claimed, "They provoked me so I taught them a lesson."
Two days earlier, farm workers had found the bodies of one of the sisters, together with that of Mr Berland. A second sister was taken to Chester Royal Infirmary but died during surgery.
The three arrived in Dover on the 6 July for a camping trip around England and Wales. They had all been shot but the murder weapon was not recovered.
Detectives had been looking for a fairground rifle and a Morris 1000 car - since recovered in Lancashire -stolen from Rhyl, North Wales, the night before the incident.
Bassett who had lived most of his life in Barlaston and lived with his sister and brother-in-law, was a publishing salesman and frustrated writer who played piano at local pubs.
A Chester inquest revealed the victims died from gunshot wounds to head, chest and abdomen.
In Stafford, the coroner recorded Michael Bassett died from carbon monoxide poisoning. The inquest heard he drank 415mg of alcohol, which would induce an alcoholic coma.
His family doctor said there was no history of mental illness in the family, but a sealed suicide note, dated May 1970, was found in his room.