Those sneaky "rogue killers" got into the Saudi Embassy, murdered Khashoggi, disposed of the body, and then got out again - all without any Saudi officials noticing! If you think that story is plausible, you are also probably eagerly awaiting the results of OJ Simpson's hunt for the "real killer."
A few additional thoughts:
Trump's emphasis on the importance of King Salman's denial is also ridiculous. The King was pretty obviously going to deny it whether he and the Crown Prince (who really runs the government these days) were responsible or not.
I can understand the argument that we need to turn a blind eye to Saudi bad behaviour because they are such a vital ally. This murder is just the tip of a much larger iceberg of awfulness that has been tolerated by administrations of both parties. At this point, however, the Saudis need US support at least as much as the reverse, and we can probably afford to crack the whip. At the very least, the president should not make a fool of himself by giving credence to the Saudis' ridiculously transparent cover story.
I'm sure it's just a coincidence that the only Muslims Trump has a favourable view of are those who shovel lots of money to Jared Kushner and the Trump family more generally.
I wonder what Prince Mohammed Bin Salman was trying to accomplish by ordering this hit. It's far from his first repressive measure against real and/or imagined dissidents. But this one is particularly "In your face" relative to the West (killing a well-known journalist abroad, one who had written regularly for the Wash. Post & other Western media). My tentative theory is that MBS wants to ensure that his limited liberalising reforms don't spin out of control in a way that undermines his power. He doesn't want to go the way of Gorbachev, and others who became victims of their own easing up of repression. Thus, MBS wants to make sure everyone realises he will NOT tolerate any attempts to push liberalisation further than he himself is willing to go. For example, women are now allowed to drive, but they better not press for equal rights beyond that. Killing Khashoggi, despite the risks involved, is a strong signal that MBS will stop at nothing to prevent the liberalisation process from spiralling out of his control.