THOUGHT being the operative word.
but by depriving them of what they thought they had
You say they thought they had, which is a problem in and of itself, but even if they did think that, it wasn't the case, they were mistaken and need to take responsibility for their carelessness. Some people who like the libertarian philosophy and claim it for themselves forget the second part of the definition. The two parts are indivisable if it is to mean anything.
Individual liberty and personal responsibilty
PS..You still haven't shown the fraud you said he used. Careful, words mean things. Fraud is a serious violation of individual rights.