Are you sure that is the whole passage?
Either I am sorry, I didn't exactly understand what you are saying in the post, you didn't make that much sense, and nor did the whole passage to some degree.
Also I assume you mean prison sentence and not poison sentence.
Firstly, I think the flaw in the argument is 'correlation doesn't imply causation', just because prison sentence were reduced doesn't mean that is the reason crime increased. It could be a increase in poverty etc.
Secondly, " Victims need to see that perpetrators of crimes are punished." is not the conclusion because it isn't being backed by the other reasons.
"heavy punishments deter criminals." therefore "victims need to see that perpetrators of crimes are punished." This does not make sense, therefore it is not the conclusion.