No one in this thread is going to accuse the individual. And no one in this thread is making any suggestions that the OP didn't already make.
This is like calling someone sexist for suspecting a husband killed his wife, upon arriving at her corpse.
No one is being racist here. That being said, no, people who grew up writing Hangul don't write like complete shit. There is nothing wrong to try and have that theory, but at least anecdotally speaking, that isn't what happens.
That's as ridiculous as someone's personality affecting their hand writing.
And! No one is being racist. "Korean" is referring to nothing but "grew up writing Korean alphabet".
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That aside. OP, please stay passive and let law enforcement protect you. Don't actually accuse anyone.