Sure, they can tell, if they look.

But people with well-developed career instincts might not want to look. I think you overestimate how much the regular policeman, coroner etc. cares about truth for its own sake. Do you really want to pick a fight with Boeing?

It's very easy to play Nelson and turn the blind eye. Making up a coherent narrative in a lie is hard. But the lie "I didn't notice anything suspect" is very safe.