You've just walked into a trap filled with metal-helmeted shield-bearing buffoons. Of course you get to kill them all.
Once you've done that, you will get another cut scene. When the cut scene is over head, walk to the first ladder.
Hit the X button at the bottom of it to pull it down. Climb up the ladder to the second level.
Hit the first gong to open the nearest door. Pulling the first lever opens the prison bars on the second level of the prison.
Inside one of the cells you will find a box of shields.
Throw a shield at the gong that you can plainly see from the first lever.
Hitting that gong will open up another door that will allow you to get to the next box of shields.
Pick up a shield from this new box, and throw it across the room at the other gong to open the last door.
Once the door is open proceed through it to flip the last lever.
Flipping this last lever will release the prisoners. Go down to ground level to finish this section.