I’ve wondered this same thing, if he’s so “criminally smart”, how in world can expect to sexually assault without leaving any any dna. It seems that dna hard to control as it seems to shed constantly in hair, saliva, sweat, skin cells, transfer from other surfaces into your clothes and easier every day to link to perpetrator. Even with gloves, total body suit, or wet suit over another. Unless his idea was to humiliate or hurt.
Thinking seeing masked man leaving house would invoke different emotions from masked man entering house alone.
Also
Would think that housemates give each other privacy, say if a man walked a housemate home after night out, and left house you would NOT expect to get housemate calling 911.
I think we will hear a lot of reasons why persons might be so tired which are not party related. Perhaps person did big 10k run the day before, or studied all night for an exam or finish a paper then went out to celebrate and looking forward to sleeping in late late late.
They will all be able to say where they were, with whom and who were texting for every minute of day til asleep. Sleeping late because house so quiet. (I’m one for thinking dog is like mine, when stressed, stays very still and quiet for days around fireworks celebrations, thunder. Doesn’t want to leave the house, eat or pee.)
BK going to rely on his big fat ZERO alibi. Zero life for days up to & after his crimes. (Doing nothing other than changing his car’s registration and showering without a shower curtain and other not quite right stuff. )
However, many rapes are unsolved every day in America, he may have thought if his DNA isn't in the CODIS they'd NEVER find him if he did leave any behind.
Or lie that they were on a date..date rape is harder to prove in a court of law...but ultimately I think his fantasy was pure sadist in nature.