That is possible, but the general rule is keep it simple. If you're right LE can possibly trace a purchase of that equipment to him. Also, they could trace the purchase of the debilitating substance some posters think he may have used. IMO he attacked blitz style and no one a chance to scream. The body goes into shock and normal reactions aren't possible or expected when in a state of shock.
Attacking them in the middle of the night when they were all in bed and likely asleep, quietly, quickly, and brutally (blitz style) with a big knife certainly seems like a huge tactical advantage, with likely anyone waking during the attacks not able to come fully awake and be too shocked to react normally.
However, 1 of the 2 people that were similarly attacked by someone with a knife in bed together in the middle of the night (around 3 am) did wake up and was able to fight their attacker off and survived: Cops probing link between University of Idaho murders and similar Oregon stabbing
In the case of X, E, M & K, since there were 4 of them and they were paired up on 2 different floors but were still possibly within earshot of eachother with open stairwell(s) and it being quiet in the middle of the night, at least X&E likely sharing a bed and possibly M&K, IMO, there would have been a more acute risk that one or more of the 4 could have been awakened in the middle of him stabbing them and/or their bedmate a few feet away, or their friend/housemate sleeping on the next floor. which seems possible based on comments about signs of defensive wounds in at least one of the victims. And in M & K's case, they may not have been in a deep sleep yet if it was indeed them making the 9 phone calls within an hour or so before LE has stated they believe they were killed.
Also, if an HVAC contractor came to their house after the killings, and presumably was ordered to check something with the HVAC system by LE for some reason, it's possible, IMO again, there was some indication from the wounds they suffered and/or where their bodies were found (e.g., people first called to the scene saying something like they'd "never seen anything like it and hope to never see anything like it again") that LE felt that degree of carnage and disarray at the scene isn't likely for the other people nearby to have been able to sleep through without cries/screams for help/calls to 911/running outside for help/or some evidence of semi-successful efforts to fight back, or there should have been time between the attacks on the 2 separate floors for one or more to have done more to try and stop him or call 911.
Which has led to speculation about them maybe all being drugged or gassed/disabled/unable to defend themselves or others nearby or hear what was going on or call for help -- to a degree that is outside the scope of "normal" within the encyclopedia of knowledge of this type of crime scene. For example, what if one upstairs and one downstairs, both of who were bigger and/or stronger than their bedmate and would have been expected to "come to" and try to fight him off suffered fewer injuries and/or had fewer defensive wounds compared to the others? This could indicate even the strongest of them most likely to be able to fight back were incapacitated by some other means beforehand (like being exposed to carbon monoxide) rather than simply being sleepy or in shock.
IMO, "the scream" a neighbor thought they heard around that time was one of them screaming while being viciously attacked or waking & witnessing their bedmate being attacked, even if it's been discounted by some (as a partier screaming or tires screeching) -- I haven't seen it be discounted as "unrelated" by LE, but I could have missed that, or LE is just not saying anything about it at this point to protect the integrity of the investigation.
They're still investigating and putting all the evidence together into a case against the suspect they have in custody with the prosecutorial team until the case goes to trial and they turn over all their evidence pre-trial, I believe, so they'll continue to be keeping mum on all details of the murders, and are doing a fantastic job, IMO. Godspeed to LE, and wishing their loved ones some small measure of comfort that LE has a suspect in custody.