Complex sentence: The medical examiner has pinpointed the approximate time of death to between 8:00 and 9:00 PM the night before, when someone stabbed him three times with a steak knife-this is based on the fact that such a knife is missing from the room service tray.
Split into simpler sentences: The medical examiner has pinpointed the approximate time of death to between 8:00 and 9:00 PM the night before. They believe the murder weapon was a steak knife-this is based on the fact that such a knife is missing from the room service tray.