I'd bet that it was a couple of lifers that did the deed.
They had nothing to lose and this was a trophy for them. This would bring them respect amoungst the other inmates.
The two men (as yet unnamed) aged 23 and 32 then cleaned themselves up, went to eat breakfast, then turned themselves into officers for the crime, which at that point had gone undetected.
They had nothing to lose and this was a trophy for them. This would bring them respect amoungst the other inmates.