Input (grade 13): Since the head wounds inflicted on Olga and Tatiana were instantly fatal, it is likely that Maria, perhaps only unconscious, was the sister who screamed, while Anastasia may still have been able to move and moan.
Output (grade 5): When Olga and Tatiana were shot, they were killed instantly, so Maria was probably the one who screamed. Anastasia might still have been able to move.