Castle nut and cotter pin missing from steering linkage suggest either neglect (incomplete reassembly after some work) in maintenance or sabotage.

Commercial drivers are supposed to do a pre-trip inspection before accepting the vehicle for the run. But even in the truck driving school I attended it was rarely given more than lip service so that one could pass the test.

(Of course most of the driving students hadn't the faintest idea what they were looking at and therefore no idea what to look FOR beyond tire tread depth.)

At first glance, that's how it appears.

Though as we all know, appearances can be deceiving. And photos can clarify or mislead; their value depends on context.

So let's not grab a rope and saddle up just yet. We will learn much more from the whole story.

You can e very sure the NPS will do a very thorough investigation of this accident. When that is finished we will know a lot more than we do now.