Complex sentence: It is believed that this position had been attributed to his sitting on the edge of the bed when he allegedly shot himself, after which his body fell back on the bed and the 9mm Luger pistol fell between his feet.
Split into simpler sentences: It is believed that this position had been contributed to his sitting on the edge of the bed when he allegedly shot himself. After which his body fell back on the bed and the 9mm Luger pistol fell between his feet.