We know from the reports that the suspect grabbed the Nov. and Dec. victims from behind. With the Dec. victim, the suspect used some sort of neck hold on her that caused her to lose conscious for a few minutes.
Consider this scenario..........................Brianna didn't go to bed right away. She was on the phone with her boyfriend at 4:23am. The suspect may have been outside lurking for some time, watching her and waiting for the opportune moment to grab her.
Just as Brianna turns out the light and prepares to lie down on the sofa, the suspect quietly slips though the unlocked door and grabs her from behind as he did the others. He puts his hand over her mouth and his forearm is gripping her neck in a hold. As with the Dec. victim, the suspect applied pressure and Brianna lost conscious. He laid her on the sofa while he quickly finds something to gag her with, and he finds the pink underwear in a pile of dirty clothes nearby. Brianna had struggled against her attacker and her lip was cut and she left blood on the pillow. The suspect uses the pink underwear to gag Brianna before he carries her out to his vehicle.
Brianna regains consciousness in the suspect's vehicle and he tells her not to look at him or he'll have to kill her. The suspect removes the gag in preparation for sexual assault, and Brianna screams and fights him. It's at this point that he kills her, strangling her with his hands to stop her from screaming.