Let's rationalize, the crime was either premeditated and Dr Sievers was the target or it was random and she just happened to be at the wrong place at the wrong time.
Random can always happen, anyone could be responsible for her death. Random could include home invasion, burglary, stalking ( while she walks the dogs for example), car accident (dents in the rear of the van), vandalism. The broken in door could be the entry point. Someone may have noticed the missing security camera to the South side of the house and took advantage. Who might have thought nobody was home? Thief, neighbor(misinformed or no particular knowledge, he sees the trash-cans from Friday still out on the curb, house is dark)
Premeditated and targeted would limit the pool of attackers to those who knew that she was at home (alone) or when she would be at home. Perhaps the attack itself was not planned as such and it was just the result of escalation. In that case we would have to consider that the fact she was home alone - if she was- might have not been part of the plan. Let's say the plan was to talk to Dr Sievers about something and the talk escalated into a physical conflict resulting in her death, then the unsub did not have to know whether Dr Sievers was home alone or not. She would have just happened to be there. Premeditated could include messing with the alarm system due to previous knowledge, the broken-in door as entry point, possibly using keys to get into the house and disarm the security system ( staged break-in would be part of the plan then) , trying to take something that was inside the house, stalking her all the way from the airport (makes no sense as they either knew she was going to be home alone, in which case they would have known where she lived and rather lurk around the house waiting for her).
Who knew or had access to the information she would be home alone? Family, neighbors, service people, co workers, patients, friends etc. .
If this was random, LE would go by evidence and chances are the burglar was already in CODIS. A neighbor trying to break in would still have to know how to avoid the security system. So that would be rather a planned burglary without targeting or planning bodily harm. He would totally panic running into Dr Sievers, make mistakes and consequently possibly leaving plenty of evidence behind.
If this was planned, the planned elements would include the way of entry, way of exit, the security system (on or not?), Dr Sievers, dogs (?), crimescene control (evidence inside/outside), noise, transportation (if needed), someone guarding the outside.
If the attack itself was not planned, but the visit was planned, then the security cameras should have come on, if the system was armed or active. If the cameras were not running, anyone known to Dr Sievers could have entered the house legally through the door. If we are looking at service people, they were misinformed about her homecoming. Service people could include the dog sitter, a house sitter, cleaning personel, security personel, a neighbor with a key, etc. .
There are many more combinations and possibilities to who and why. Without evidence we cannot exclude anyone. Unfortunately we are not privy to the information needed and engage in including suspects,when we should be really excluding them or finding reasons to exclude them.
-Nin
