With all the mistakes made outside the house, how could he be so meticulous inside the house?
Factor in that it was done in such a small window of time and with at least one victim fighting back (if not more). I believe there will be more evidence inside the house that hasn't been included in the PCA.
MOO
SPECULATION/theory below
My theory on that is that planning a crime of this time was an every day obsession for BK. He was incorporating more and more of his knowledge about crime into his theorized "perfect crime." I have interviewed many non-murderers (people in jail for attempted murder; serial rape; breaking and entering, etc) and many of them fantasized about homicide/larger crimes. Indeed, even so-called petty criminals (the ones who sneak onto people's porches and steal packages) are often thinking about other crimes.
BK was thinking about crime, all the time. It is my view, based solely on what SG said before he quieted down, that the murderer in this case researched and practiced how to use a knife and how to use a knife in such a way as to eliminate screaming and to minimize blood spatter (as SG says, KG's wounds were large slash wounds; he says the coroner says that "slash" was a better term than "stab.") What the slash method accomplishes is rapid blood loss (some of it initially into the inside of the body, particularly the lung injuries) but it also results in less splatter. Choosing the lungs and the liver results in way less arterial blood spurt to the outside of the body, if the killer knows at all what he's doing (checked where the liver and lungs are and memorized a little anatomy).
Did he make his decision to act out his criminal fantasy as he left Pullman that night, angry and probably enraged by recent difficulties at school? He had readied his car weeks or months before? While he thought his plan would keep himself mostly unbloodied, surely he had to plan what to do about the car?
One scenario that fits quite a few facts in this case is that he did indeed murder MM while she was still in bed. Whether KG was there initially or not, we do not know (and we also don't know if she owned or rented her furniture in her room or was just using what came with the house). If KG came in as BK was murdering MM, then her wounds would be different as she would not have been beneath the bed covers and completely on the mattress. We don't know these details.
If, as so many believe (including SG, apparently, who knows more than we do), KG was actually sleeping in the same bed as MM, then he has both victims where he wants them - underneath blankets/comforters and on a big blood-absorbing mattress.
Squeamish people might want to stop reading here.
Sure, eventually, there would be blood dripping from the mattress, but initially, arterial blood spurt from the lung wounds would have been mostly contained by bedding. The Marine training videos and written materials on how to use this type of knife to kill indicate that leaning on the knife (plunging, not stabbing) is most effective and the least bloodying for the killer.
So he's wearing some kind of coverall, easy to remove rubber-soled shoes, and has a trash bag in the trunk of his car. Or a trash bag on the ground near his car. He didn't count on Xana fighting him off, but so far, we have heard of no mention of cuts to the visible parts of his body (we don't know why he went to the doctor or what parts she saw). Like everyone else, I hope he needed wound car items from Albertson's, but I'm not holding my breath on that.
He's wearing a mask and likely a beanie or something. Each victim is incapacitated and dying within 15-20 seconds of his attack. As far as we know, Xana is the only one on the floor - and so, her blood is not being absorbed by the mattress. It's likely her blood that was on his one foot. He also apparently spoke to her and had to attack without her being asleep/lying down/nearly asleep.
So I hope that Xana will be the one whose blood is found in the car.
I do think he was more methodical (I have a hard time with the word "meticulous" for any bloody murder) inside the house, but had some kind of system rigged for keeping potential blood evidence contained in his car. I hope his system failed.
Indeed, I think he's smart enough to have been double gloved (nitrile), taken off coveralls, shoes and socks if any (probably didn't wear any) and stuff them into a waiting garbage bag. If he's smart, he disposes of the two pairs of gloves in different places (and puts them in baggies?) and puts new gloves on to drive his car. The trash bag has to be somewhere (the trunk?) but the clothes and shoes inside contain very little blood. The blood on the shoe is already invisible to the naked eye.
I think he was very concerned not to get bloody and sadly, it's possible the car will yield less information than some have been speculating. So this is my counter-speculation. It is the digital forensics that are going to convict him, IMO.
Speculation. IMO.