I'm not real sure how to take your question, as far as the defination of "false inprisonment" that would be: A detainment, or arrest of a person without a warrant, with an illegal warrant, or with a warrant illegally executed.
I assume that an inmate has told you that he/she is in prison under false imprisonment, which I would think would be his/her way of saying that they are not guilty of the crime, or that there was a glitch in the legal system as to the way that this person was sent to prison/jail.
There are really alot of different things that could mean, if you want to explainalittle more as to what the situation is, then I might be able to give you a more deffinate answer.
Best of luck in your search to find the answers !!