They were on a special program learning maintenance at the prison. They were given tools and access to the catwalks to do work on them with contracted people. they were practically outside the minute they started that job after going back there.
In regards to the fabric guitar case, it was flexible and held a lot of things and looks like it was used as a suitcase for all the tools. it had to be dragged through maybe between them, or tied to them. Most likely pushed along the tunnel. They needed it to cut the final lock/chain to the sewer. It probably also served as a carry all for clothing, food etc.
They were probably given the pliers etc because they were part of the program and the CO probably thought nothing of it. Getting through the brick wall is still pretty mind boggling, the one after the catwalks. I sent a link to what an acoustic guitar case looks like.
http://phitz.com/products/acoustic-guitar-case-original-fabric-ph72505fsa-burgundy-velvet
Just a theory FWIW