Bryan Kholber didn't plan the crime well because if he did he would have known who was home and most likely didn't plan to kill all those people. The problem with all the criminal profilers you see on TV talking about the case is they are/were not criminals and can't think like one….Being a former criminal I DO!

To begin with, Moscow Idaho is a college town and as such there are continuous parties at Fraternity and Sorority houses every night. In all likelihood Bryan Kohlber attended many of those events and ran into the two girls several times and it's reported he had been text messaging one of the girls and hitting on one of them and was enraged  after being brushed off stroking his anger and insecurity.  

Here is a theoretical chain of events based on me being a former criminal planner for Organized crime as to what actually took place INSIDE THE HOUSE! 

Ethan and Xana Murders

The house was dark and when he made entry he came inside looking for one of the two girls. He went up the stairs and on the second floor entered the wrong bedroom where Ethan Chaplin and his girlfriend Xana Kernodle were.  As they were probably awake and not knowing what to do as it wasn't part of his plan …he impulsively killed them both. It's sad because they became collateral damage and were not planned murders. 

Madison and Kaylee Murders

He went up the stairs to the third floor into the second bedroom not knowing that two girls, Madison Mogen, Kaylee Goncalves, would both be in there, so it's hard to determine which one was really his target. Since they were both there…he had no choice but to cover his tracks and identity so he killed them both. So one of those girls was collateral damage. 

After the killings Kohlberger had high anxiety and wanted to get the hell out of the house in a hurry. Keep in mind It was a dark house and the roommate who saw him was half asleep herself and all she saw was a figure passing her not knowing what room he was coming from unless she was already on the second floor

If he had come to kill multiple people he would not have hesitated and killed the girl in the hallway. 

I know all this because that is what I would have done!