I'm more on he did it as opportunity arose. And for the his own pleasure, and then had to (excuse my words ) get rid.I suppose there is the grim possibility that she was stolen to order, abused by the payer (and possibly payee too) and then murdered by the latter, and the gruesome episode possibly also monetised on the dark web. Seems a complicated scenario and much more likely imo this was an opportunistic crime, possibly undertaken without much forethought given to an exit strategy. Effectively disposing of the evidence would be the only way to minimise the likelihood of being caught. IMO
I don't think anyone else involved imo