Most People In Prison Think They Are Basically Good

God said that the Ten Commandments were given to show the unbeliever his sin, God calls them a "school master to lead them to Christ."

We are to show the unbeliever that they are sinners, in order to do this we must repeat God's judgement upon their lives.

Many non-believers think they are good, even the ones in prison. 

When we shine the light of the Ten Commandments on their life, they can see, if they choose to see, that they are sinful and helpless and in need of a Savior. Without this knowledge they cannot come to Christ.