Well the reaeon why i don't think he is a infp is because he lacks fi. And ginkgo seem to agree that he is a infj too (his being an infp coukd probably relate if he is indeed an infp).
It's not inly hard for fi doms to reconstruct their ethical perspectives. Others would find it hard too, especially if it's such a drastic shift. Ethics aren't limited to fi users and fe users aren't fickle with their ethics either though fe loathing fi advocates would like to think so.
I would't say that is the only reason he can't bring himself to kill hannibal. That was a bold assumption to support your claims
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Brb work.....
Edit -
Taking your own point of why will not killing hannibal (look above) sounds quite anti fi. He needs to prolong what he 'has' to do because the person he 'has' to kill is the only one who could help him and he 'would' prolong the matter until he gets what he wants doesn't sound very fi does it?
I wouldn't say it sounds fe either but fe could take a breather and adapt until the right circumstances are available to take action. Actually Je would. Not just Fe.
There is a dexter thread. I would like to see your arguments taken there. Most people think dexter is a istj because.of his code.
However i must confess that envisioning the scenarios is the second reason i assumed ni.