In an interview with Heinz Prüller published in Grand Prix Story 1972 of which I have a copy, Marko himself says it was a stone thrown up by Peterson's March. This is a very quick and so probably a bit clumsy translation of an article I wrote about Helmut
...elsewhere on the circuit the onboard extinguisher in Peterson's March has exploded. With ice cold feet the Swede races on and passes Marko's BRM on lap eight. Helmut remembers: "Peterson was very much on the limit and he drove through the dirt on the edges of the track quite unneccesary." Marko sees the stone coming, as big as a fist, ducks into the cockpit, but then he feels a terrible pain. When he looks up again, he sees he is heading for the guardrail and throws the BRM into a spin. He jumps out of the car, takes his helmet and balaclava off and gesticulates desperately to the marshalls standing nearby. As they dont respond he runs towards them, shouts for an ambulance and then he collapses. Luckily Vic Elford arrives in one of the Porsche 914's [these were placed along the circuit to help out in case of an accident] and rushes Helmut to the mobile hospital in the paddock. From there he is sent on to the Hotel Dieux hospital where - although he can barely stand on his feet anymore - he first has to fill in forms and declare who will pay for the costs of the operation. Only then the doctors tell him they cant help him, that he has to go to the St. Jacques, an eye clinic. He is alone in the ambulance driven by a maniac: Helmut has to hold on tight not to fall off the stretcher in the back. After the operation in St. Jacques the doctors ensure him all will be fine and that he will be able to race again. With his wife Irmi, who had rushed to France after hearing about the accident, Helmut flies home relieved, but in the hospital in Graz doctors discover that his left eye is not going to be okay at all and he his hosptialized again.
Edited by Formula Once, 19 November 2010 - 23:41.