This question already has an answer here:
I'm looking for a single word of phrase to describe someone intentionally acting dumb or intentionally over looking something obvious so they can deny responsibility or prevent themselves looking bad.
E.g. A person states that they hadn't consider that don't something would have an knock on effect that when the effect is completely obvious and was unlikely to have been overlooked.
I've seen the following suggested: "deliberately obtuse", "passive aggressive" & Blonde in a similar query on Yahoo, but it's not quite what I'm looking for.