Not being a human might indeed be a valid legal defense though! I doubt the law or case history is very clear on that point.

I'm only responding regarding who "they" refers to, not about whether it excuses them.

Pretty sure if they have the technological capacity to travel from somewhere to earth and land undetected ... they don't have to care about any human laws.

I’m not convinced. Some economist wrote a thing about how if aliens observed us they would think dogs and automobiles were our rulers cause we spend all our energy taking care of them.