Exactly. The fact that 1) he has a face we can identify with, and 2) they lured him into an official establishment of their government and then killed him in cold blood. A place where you might otherwise expect the rule of law to prevail.
Yeah I understand that, what I mean is that from our perspective a person should be able to walk into a government office and be safe from extra-judicial sanctions. So a Saudi national may not feel that safe themselves, but it is harder for someone from a Western-style liberal democracy to intuitively understand and is therefore horrifying.