really care about it. if they run me out, i'm going to leave before they do punishment or the reprimand on me. >> cardenas starts with some wire scavenged from some electric hair clippers. >> we rub the wire like this here. >> he winds the wire around the screw to make a crude electromagnet but he also needs a metallic magnet which is pilfered from a phone or speaker. >> the magnet, when you put it on top of the screw, it bounces with the cycles of the electricity. you bounce like this. >> the needle is made from a staple attached to a q-tip shaft. >> and then you use soft string to tie it up. that's pretty much how you do it. the magnet when it bounce, it push the needle. i don't invent it but i learn it. >> several other bexar county inmates also make their own tattoo guns or rigs, and the source of their knowledge could very well spring from just one man, jose hidalgo. >> early on in his incarceration he was teaching the other inmates how to create these tattoo rigs, how to do the tattoos, and as a result they were destroying county property.