He may not have realized he was spotted by one of the roommates. (If the house was quite dark at 4am, someone peeking out from a darkened bedroom might not be easily visible, especially if the victims' bedrooms were better lit, meaning the killer's eyes might not have adjusted to the darkened...
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Quoted from excellent WSer JumpingJackFlash:
Such good questions. I think they sat down and thought it through carefully. They knew they wouldn't have enough for a PCA for many days and a material witness whose life would be put in danger as long as the Monster was still out there.
So, they did a lot of things to protect their witness(es). They misled him. It was intended to mislead their suspect. They also said they didn't have a suspect. This is pretty common in the investigation phase, but also the reason why we, the public, expect to see PCA's and.or AA's released to us.
The statement about not waking up until later that morning is a fib, for sure, but not a lie if in fact D went back to sleep (which I predict she did - she may have thought the guy leaving was the DoorDash guy, she may have been almost asleep throughout the described events, she may have huddled in her bed and fallen asleep inadvertently while intending to wait a decent amount of time to go investigate - no one would be thinking about a mass murder, I don't think).
I think there's a pretty good list of details that have been suppressed (some not in the PCA, of course) or misrepresented. Year of the car. Acting as if they didn't already know its plate. Basically, everything they saw on those three neighborhood cameras (which they did mention - but I bet by now there's even more camera footage).
The main reason is that early on, BAU and others (common sense to some extent) said that this particular murderer was at high risk for 1) suicide; 2) suicide by cop with possible death of LE; 3) murdering a witness; 4) murdering someone else; 5) murdering someone he believed to be a witness; 6) destroying more evidence than already disposed of - he still had his computer, for example.
#3 is of course their main concern, but D was quickly sequestered and was not going back to the area (and may never go back, we don't know). The others are major concerns as well. Also, they gave him time to turn himself in, hinted strongly in ways he would understand that they knew who he was, etc.
As it turns out, BCK has been able so far to contain himself (is off suicide watch; he hasn't got bite marks on his hands; he hasn't rammed his head into a wall; didn't try to bite officers, etc). He looks apprehensive when stopped by the InSP for sure, and not quite himself, but is currently in a relatively normal frame of mind by all appearances. LE did their job very, very well. 1-5 did not happen and even 6 on my list seems to have been partly accomplished.
They're going to find victim DNA in his car, is my prediction. And stuff on his computer.