I am trying to look for a word, gesture or expression that represents a state of confident not knowing. So far I am using a shrug for this but when used often it starts to come off as very apathetic which I definitely don't want. I have found gestures for being confused, uncertain etc but they don't quite fit because they don't capture the vibe of knowing confidently that you don't know the answer. Consider when being questioned and you want to make it very clear that you are certain you don't know the answer, not that you couldn't care less. The only thing I have thought of so far is a head scratch but this again doesn't communicate much certainty.
The policeman looked sternly down at John, "Mr Smith, where was Nigel between 4 and 6pm on Sunday evening?"
John shrugged, "I swear I don't know officer, I was at a work function until 7pm that night."
"Do you still love me John?" asked Mrs Smith.
John shrugged, "Honestly, I don't know anymore."