Question: When the guards are talking to Percy in the restraint room, Paul says he knows he sabotaged Del's execution. Why did he let him get away with it?
Chosen answer: Percy's aunt is married to the state Governor, giving Percy powerful connections. All it would take is one phone call from Percy and Paul and the other guards could lose their jobs and if Percy wanted to, never find jobs again. Something Paul or his friends didn't want to happen.
The characters talk about this several different times in the movies, how political connections can ruin careers.
Answer: In addition to previous answers, it is probably also worth mentioning that they will never be able to prove it. Percy mentions multiple times that he "didn't know the sponge should be wet," even when they are back in the Green Mile and only Paul and the other guards are around, indicating that that will be his defence when they ever make it into a thing, knowing that they will never be able to prove otherwise.