PARIS, France - French investigators have ruled out any third party involvement in the ski accident of injured former Formula 1 driver Michael Schumacher and have closed the case, local prosecutor said.NO FOUL PLAYAlbertville prosecutor Patrick Quincy said: "The investigation into the causes and consequences of the December 29 2013 skiing accident of Michael Schumacher has been closed. No person has been found guilty of any violation."Schumacher (45) has undergone two operations since sustaining brain injuries after hitting his head on a rock while skiing off-piste in the French Alps resort of Meribel. The seven times world champion was in a stable but critical condition until late January and doctors in the Grenoble hospital have started waking him up progressively by lowering his sedation.The investigators tried to determine if any third party was responsible for his accident and if Schumacher was aware that he was skiing beyond the marked-out zone.The prosecutor said: "Signalling, demarcation and information given on the limits of the piste were in line with the French standards."Schumacher, who quit the sport in 2012 after a disappointing three-year comeback with Mercedes following an earlier retirement from Ferrari at the end of 2006, won a record 91 grands prix.