Ok, here goes I'll try to be as specific as possible. Made in late 90's early 2000's. The movie centered around an amulet (or necklace) found outside USA and brought to old half abandoned prison, when the wearer got away by acting like he was a prisoner so he could be kept safe by prison.
Somehow a monster revolves around the amulet, either protecting the wearer or calling the beast to come kill. I remember that in the prison they had to go on work detail to clean up a room with a lot of boxes. Some prisoners wanted to escape.
I remember one young actor was a hacker who got sent in for hacking. He said he would lead them out, but when the beast came, he slipped out. He was later killed by the beast. The hacker's actor has been in other movies and plays bad guys mainly. I remember the ending was when the prisoners were freed and one came out wearing the amulet (necklace).