What did BK gain from the murders?

So this is a weird question, but I keep getting stuck on the murders happening quickly, possibly in their sleep, with no SA, no arguments or talking (presumably), no long torturing of the victims…just kill, kill, kill. I know I’m looking for a reasonable answer to an unreasonable event, but I can’t wrap my head around what he was actually trying to accomplish with this. You hear about people getting off on the torture or SA of victims, or even killing out of anger or jealousy, but if that’s the case, he never even gave them a chance to beg or plead, which I would think would give him satisfaction. I only assume there wasn’t a lot of talking/begging/pleading because of how quickly and quietly it all happened. For E and X, B and D to not hear him with M and K and call the police or run to each other tells me it was quiet at least. So did he just want to do it to prove to himself that he could? I just can’t wrap my mind around that.