The Prison Juggernaut is one of the toughest monsters in the game. Watch out for its melee attacks that do a tremendous amount of damage. If you have the ammo, shoot him with your pistol or shotgun. After defeating the Juggernaut, enter Wing B of Block A3. To your left, there is a locked gate. Break the gate and cross through. Walk towards the direction of the loose electrical wire. 

Silent Hill: Downpour Juggernaut

As you move through the cell, a juggernaut grabs you from behind. Break Free. Run past the exposed electric wire, and as the Juggernaut chases you, the wire touches it and it is electrocuted and falls to its death.

Your current task is:

Escape from the prison
No! This can't be happening. I was out, I was FREE. Why am I inside again? This isn't Ryall, or even Wayside. What more does it want from me? I won't let it break me. MUST. GET. OUT.

Enter the cell to your left, and flip the switch to cut off power to the exposed wire. Use your access card to unlock the door to the security room. Check that room for various useful items, including a quarter dollar, a first aid kit, and a shotgun.

There is also a cabinet, open the drawer to find a BOLO Alert:

POLICE DEPARTMENT
Boston Police Department
For Immediate Release
August 17
BPD SEEKING PUBLIC'S ASSISTANCE IN LOCATING INDIVIDUAL SUSPECTED OF CHILD MURDER
The Boston Police Department has issued a "Be on the Look Out" (BOLO) alert for (striked out) in connection with the murder of a 8-year-old male. In the BOLO alert, the BPD expresses interest in locating and questioning the suspect and asks all law enforcement personnel and civilians to notify the BPD immediately if he is located. Suspect should be considered armed and dangerous.

Examine the controls. Press the big red button. The light will turn green, and on the monitor you will see the checkout zone.

Exit the security zone, then go out and back across the walkway, into the Block B checkout room (green light bulb above entry). Use your access card to unlock a door to your left.

In a locker, you find the following article:

Crime & Law
OVERLOOK PENITENTIARY -THE PRISON OF NO RETURN
By Paul Grim
In operation for more then 50 years, Overlook Penitentiary has garnered a reputation as a place where prisoners are sent to never to be seen or heard from again. But that's not all, Overlook has also been rumored for decades to be haunted. Strange, disembodies voices, ghostlike apparitions, gruesome deaths, and unexplained disappearances, the inventory of peculiar happenings that have been reported over the years by both prison staff and inmates is disturbingly prolific, some might say. Others, however, claim this is nothing more than legends born out of an environment that is conductive to terrifying tales.
"No question about it" Warden Steven Crevitson told us. "This can be an extremely scary place. We've got society's worst of the worst locked up here, many of them clinically insane. It's just a matter of time until crazy stories flow out of our prison, regardless of how impossibly horrifying they may sound".
Despite his doubts about the paranormal aspects of Overlook, Crevitson does admit that some portions of the prison's notorious reputation are not wholly undeserved. Over the years, there have been numerous reports of strange deaths within Overlook's foreboding walls, and even more bizarre disappearances. And although a number of these incidents remain unsolved, Creviston maintains that the vast majority of disappearances are easily explained.

In another locker, find a first aid kit. Enter a small cell and in a drawer find a map of Block B.  Press another button in the control room to turn the light green and open the next door. As you approach the exit from the checkout zone, you cross through a metal detector and the door shuts. This is a PUZZLE

Silent Hill: Downpour Metal Detector Puzzle

Solution to Prison Checkout Room Metal Detector Puzzle
Note the two windows on both sides of the metal detector. The guards can pass their sidearms through that window. The metal objects in your inventory are triggering the metal detector and slamming the door shut. Go back to the control room, unequip and place all metal items on the checkout counter. Then go through the metal detector again, and pick them up. You can now exit the checkout zone.