How about a more recent killer from Japan, Takahiro Shiraishi? He's the kind soul who helped young girls who wanted to commit suicide, make their dreams come true. He killed eight girls (three high school age) plus one boy.

He was apparently a fan of self-asphyx, so he knew how to drug and strangle his willing victims, then let them wake up as he was having fun with them. He said "None wanted to die actually". It sounds like he may have bashed them in the head as part of his fun. He called them "objects of desire". But he isn't giving out all the details unless he gets paid. GoFundMe, anyone?

He confessed and pleaded guilty and is waiting to be executed. Wikipedia says he's not dead yet, so there's still time to get those bitcoins together.