The Alma Mater State Prison is a prison located on the south-west of the Residential District of Anywhere City. The prison is on an island in wich you can only get there by using a ramp (since the doors are closed, you need to use a glitch to ramp to the top of the prison and then get inside the prison).
Alma Mater means "nourishing mother", and it's often used as a school or university name.
In the mission Penal Ties!, Billy Bob Bean wants to revenge the Alma Mater guards because of the bad times he had there and asks Claude Speed to find some Beany Liquor with an illegal dealer, so he gets arrested and gets inside the prison. There, Billy Bob tells Claude to find "the Hump" to get instructions for Claude about where to get a cop uniform and a machine gun and also gives him emergency keycards. After claude gets the uniform and the gun, he shoots and a riot begins on the prison. Billy Bob then tells claude to kill the 8 guards when the riot starts. After all the guards are killed, Claude uses the emergency keycards to blow up the generators and open the prison gate and then uses a Special Agent Car to escape from the prison. When Claude escapes, he gets 3 cop heads of wanted level and needs to run to Disgracelands to change clothes before the cops get him.
You dont get wanted level by killing the prisoners or the guard on the prison. After the mission ends, the gates are still open, meaning you can get on the prison by car at any time then.