No-one who plans to kill also brings a sheath and unsheathes said knife in the middle of committing his crime. It's very hard to ascertain what Bryan's goal was but given his movements it is probable that he had a very specific victim in mind (most likely Maddie) and everything else that happened was the scene going completely out of his control. He most likely didn't expect Maddie and Kaylee to sleep in the same bed which ruined his goal of raping or killing Maddie (or Kaylee) quietly, then he probably didn't expect Xana to be awake at 4:00 AM and he most certainly didn't expect Ethan to be there.I think we're circling the truth.
No one puts a bloody knife in a sheath. I mean, maybe you do if you know you're going to bury it...
IMO he left the third floor fully intending to use the knife on whoever was awake below. It wasn't until he left XK that he might have realized he didn't want to drip blood all over...
Realistically, it's like the sheath served its purpose, it got him in the door, blade protected.
I wonder if someone could re-enact that hand placement. One victim. One assailant. Pulls the knife out of the sheath, that hand goes to the bed for leverage, the other hand has the knife, thrusts/plunges, but suddenly there's a second victim, hand comes up leaving the sheath on the bed.
FWIW I don't think he ever planned to put a bloody knife back in the sheath.
Doubt it bothered him. He thought he'd cleaned it.
JMO
Generally speaking I am of the thought that he just wanted to murder Maddie quietly, slip out of the house leaving no evidence and then have the police waste their time focusing on the other roommates. By the time the police have removed the suspects and started searching for something else, his trail would have gone cold. I am also in agreement with SG that Bryan rushed this as he was frustrated that the number of times he went there the roommates were occupied. While it does seem like a planned crime, it also seems like something he did in a spur of the moment given his somewhat aimless driving minutes before deciding to park behind the house.