The Legal Flexibility of Double Jeopardy specifically in the movie FRACTURE?

In the movie Fracture a man shoots his wife who lives and is in a coma. He is charged with attempted murder. He is aquited on grounds of not enough evidence. Later he then uses his legal power of attorney to kill his wife by pulling the plug. At the end he is charged with murder in the 1st degree even though his shot was not the couse of death. She was killed legally and therfore he should not of been able to have been charged with murder. In addition a doctor reported that she would of actually outlived her husband. Since the shot had nothing medically to do with her death and her killing was in the peramiters of the law is it legally posible to charge the man with murder in the 1st degree.