. >> wabash valley's secured housing unit or shu holds the prison's most dangerous inmates. >> why did you come back after that? >> you have to. you absolutely have to. if you let something like that stop you, then they win. if some of them were out on the streets, i would pity anyone they came across. >> but some inmates feel the shu only fuels their violent tendencies. >> the shu is terrible. it is a terrible place. i wouldn't wish this place on my worst enemy. >> as a shu inmate, billy brown is confined to a solitary cell. >> 24 hours, we sit in this cell without communication, without contact from any other human besides officers. >> it's a windowless cell in a pod, and he said this incredible thing. he says, do you know how long it's been since i've seen a tree? >> the last time i saw a tree? oh, man. years. it's been years. years. it's been years since i saw a tree. one of the last time i interacted with some people? years. >> but some of the staff here believe brown earn sed his term. serving a 40-year sentence for rape, brown landed in the shu when he assaulted an officer at an

inmates commit acts of violence against other inmates or staff, they're sent to the security housing unit or shu, in what is essentially a prison within a prison. inmates like jeremy towner spend the majority of their time in an 8 by 12 cell. >> the first words i ever heard from another inmate was welcome to hell. it was a zoo for men. >> our producers were granted an interview with jeremy under strict supervision of the officers because of his violent history. >> ten days was our orientation to stay in the cell, i guess. then after the ten days were up we were allowed to go to yard. we met some of the other inmates and they told us that there is a structure to live in, you know. whites live with white, hang out with whites on the yard. you don't deal with any other race. the fact we were lifers, we were probably going to have to stab people. first thing that got into my head was, we better get some knives. living on the street, you learn one thing. you survive by any means necessary. you do whatever it takes to get out of a situation like that. so if that means i have to become an accomplice, s

. >> within the 275-acre penitentiary is the security housing unit known as the shu.in a prison. shu inmates spend about 22 hours of every day in solitary confinement. locked up in an 8 x 10 windowless cement cell with little human contact. inside the shu are about 1,000 level-four prisoners, what boyle calls the worst of the worst. inmates that other wardens don't want or can't handle. dangerous gangs founded within the penal community. >> because of their gang leadership, they have the authority to authorize other people in the community or the prison to commit these types of crimes. >> and on that day two alleged gangs go to war. it's sunday, and it's raining. 200 shu prisoners are released into b yard for exercise. boyle says that the entire prison is on edge dating back to a smaller racially charged riot six months earlier between two gangs, the southern hispanics and the black guerilla family. >> you could feel the tension. staff were particularly alert. as it went on, the tension got more and more and more pronounced. >> the pent-up tension finally erupts. >> j