Biden is a laws-and-procedures man; one for the status quo. It’s why he’s getting a lot done in the US. It’s also why, short of agreeing that heads of state should be prosecuted in abstentia for crimes in foreign nations, he has no choice to admit that a foreign head of state is due immunity from prosecution. He’s told MBS that he holds him personally accountable, according to the article. But Khashoggi is a (very) unfortunate pawn in this game, and the only other three options are to kidnap, try, and jail/execute a foreign leader, place sanctions on or cut off all ties with one of the richest and most economically powerful [and nominally one of our few middle eastern allied] countries, or go to war and nuke the entire palace from orbit just to be sure. None of those three are viable - practically or politically - and so he’s fucking stuck with what he has.
There are, of course, inadequate solutions like not allowing him personally to arrive or transit the US, but that’s a bullshit limitation for someone worth half a trillion dollars and does nothing to stop him from killing again or bring peace to the Khashoggi family.