the meaning of "dumb question", "far into foul territory", "let it pass"

[kjc0123]

What is the meaning of "dumb question", "far into foul territory", "let it pass" in the following sentences?

 

"What's in the bag?" the cop asked. 
It was a dumb question, far into foul territory, and for a split second Ray, the law professor, considered a lecture on stops, searches, seizures, and permissible police questioning. He let it pass, though, and smoothly delivered the prepared line. "I played tennis tonight at Boar's Head. Got a bad hamstring, so I'm just walking it off. I live over there." He pointed to his apartment two blocks down. 

[jno]

It sounds as though police aren't allowed to ask this sort of question - too intrusive, as it would mean they could stop anyone in the street and demand to search them. So a dumb question is a foolish one; foul territory would mean illegal territory (in baseball, a foul ball is one not pitched in the right place), or just 'very illegal'; he let it pass means that he didn't protest or draw attention to it.

[rampart]

dumb question: I think in this story, the "dumb question" was a question that should not have been asked because asking the question could cause a problem.

far into foul territory:  The person who asked the question should not have asked it. The question asks for answers that the person should not know or does not have permission to know. The question is inappropriate. "Foul territory" could mean several things, perhaps in this case something illegal. The person asking the question might be breaking the law by asking. I can't tell from the passage. Foul could also mean dangerous.

Let it pass:  Ray did not like the question and he wanted to say something, but he did not say anything. He "passed" on saying anything.