Michael Stephens was a prisoner and bodyguard of Big Figure in Sing Sing prison. Under Big Figure's orders he first kills fellow convict Lawrence who's body blocks the cell's lock by slashing his throat with a utility knife. Michael then uses a welding torch to break into Rorschach's cell. Rorschach then broke the toilet and let the water flow out, making contact with the frayed power cable of the welder, electrocuting Mike.
In the motion picture, Michael wields a large electric saw instead of a welder, however the scene plays out much like it does in the graphic novel. He also uses the saw to cut off Lawrence's arms when the hulking convict is in the way of the cell's lock, killing him.