My conclusion has to do with the hammer itself. I do not believe that Dr Sievers would let in any person known to her with a hammer in their hands.
If anyone came to visit her that night or morning, then that individual or those individuals did not carry a hammer with them. There are glass windows in the entry area. She would not open the door to strangers like that. That hammer was either picked up in the house, or it was brought in.
If it was picked up in the house and used to kill her, then the perpetrator would have left the hammer at the house and not risking to run away with a bloody hammer (murder weapon) in his hands, especially if he had to jump a fence - if he did (remember the cadets were searching the entire area way up to the dog park).
If the hammer was brought in from outside, then most likely the unsub broke into the house through the side door. If that had happened, he would not have left the hammer at the crime scene, because it could have possibly been traced back to him. That's why I asked in the beginning of the investigation, where is the hammer?? I think they found the hammer and that's why it wasn't going to be a problem later to have Dr Sievers's body being cremated.
If they found the hammer at the house, they will know, if it was used to pry open the door. They might also have plenty of evidence left on the hammer itself and at the crime scene, BUT THE EVIDENCE ON THE HAMMER MIGHT NOT MATCH THE OTHER EVIDENCE LEFT BEHIND AT THE CRIME SCENE.
That is what I think about the "hammer".
-Nin