Corrected entry: It makes no sense that everyone believed Tommy was trying to escape when he was shot. There are no guards in the guard towers at night, and if there were, there would be a guard in every tower, meaning another guard would've seen Hadley shoot Tommy.
MikeH
20th Jun 2016
Correction: Hadley and the Warden wield considerable power at the prison. They didn't need to convince everyone, they just needed a plausible explanation if there was a police investigation. Hadley could easily intimidate the guards and prisoners into remaining silent.