Problem: an overseer won’t see the AI which kills us all thinking about how to kill humans, not because the AI conceals that thought, but because the AI doesn’t think about how to kill humans in the first place. The AI just kills humans as a side effect of whatever else it’s doing.
Analogy: the Hawaii Chaff Flower didn’t go extinct because humans strategized to kill it. It went extinct because humans were building stuff nearby, and weren’t thinking about how to keep the flower alive. They probably weren’t thinking about the flower much at all.

More generally: how and why do humans drive species to extinction? In some cases the species is hunted to extinction, either because it's a threat or because it's economically profitable to hunt. But I would guess that in 99+% of cases, the humans drive a species to extinction because the humans are doing something that changes the species' environment a lot, without specifically trying to keep the species alive. DDT, deforestation, introduction of new predators/competitors/parasites, construction… that’s the sort of thing which I expect drives most extinction.
Assuming this metaphor carries over to AI (similar to the second species argument), what kind of extinction risk will AI pose?
Well, the extinction risk will not come from AI actively trying to kill the humans. The AI will just be doing some big thing which happens to involve changing the environment a lot (like making replicators, or dumping waste heat from computronium, or deciding that an oxygen-rich environment is just really inconvenient what with all the rusting and tarnishing and fires, or even just designing a fusion power generator), and then humans die as a side-effect. Collateral damage happens by default when something changes the environment in big ways.
What does this mean for oversight? Well, it means that there wouldn't necessarily be any point at which the AI is actually thinking about killing humans or whatever. It just doesn't think much about the humans at all, and then the humans get wrecked by side effects. In order for an overseer to raise an alarm, the overseer would have to figure out itself that the AI's plans will kill the humans, i.e. the overseer would have to itself predict the consequences of a presumably-very-complicated plan.
The first thing I imagine is that nobody asks those questions. But let's set that aside.
The second thing I imagine is that somebody literally types those questions into a GPT-3 prompt. Obviously that does not result in the AI giving its actual best-guess answers to the questions, but it doesn't result in the AI thinking about how to deceive humans either. It just thinks about what text would follow that question if it appeared on the internet somewhere. And then I imagine someone with a bunch of interpretability tools saying "yup, it's just thinking about what text typically follows this question", and then that person's boss is like "great, it's not trying to deceive us, guess we can trust the answer", and they both just haven't really thought of the fact that the AI's response-text does not have anything in particular to do with whether the AI is aligned or whether they'll be happy with the outcome or whatever. (It's essentially the same mistake as a GOFAI person looking at a node in some causal graph that says "will_kill_humans", and seeing that node set to 99% False, and thinking that somehow implies the GOFAI will not kill humans.)
Now, presumably future systems will train for things other than "predict what text typically follows this question", but I expect the general failure mode to stay the same. When a human asks "Are you an unaligned AI?" or whatever, the AI thinks about a bunch of stuff which is just not particularly related to whether it's an unaligned AI. The AI wasn't trained to translate the literal semantics of questions into a query to its own internal world model and then translate the result back to human language; humans have no clue how to train such a thing. Probably the stuff the AI thinks about does not involve intentionally deceiving humans, because why would it? And then the AI gives some answer which is not particularly related to whether it's an unaligned AI, and the humans interpret that as an answer to their original question, thereby deceiving themselves.