try create it's again with the same name and jailed shell enabled. then turn off shekk access for this accounts and check are they listed in vrtfs. if they not listed you can delete his accounts without problem. this waw is easyst and safest.
if it is not help you, you will need very carefully check what listed in this accounts folders on virtfs. most likely you will found some symlinks to system folders and/or files. you may unlink it. but this is hard way and you will need do any action here very carefully.
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