On the fateful night, the police officer said there was no sign of a big physical fight. Nor did Terri have obvious signs of physical beating that night (that we know of).
We do have the occipital fracture, rigid neck and probable bruises to the throat. The first two would not have been visible to the police officer, maybe the third, especially if she was face down. Those injuries suggest that Michael was on top of her, holding her down while pulling up on her neck (possibly with his forearm) and putting great pressure on the back of her head. This would account for everything except the fractured femur. That could have been twisting her leg when she went down, or him kneeling on her thigh with all his weight as he held her.
Does this make sense to you?