He should also learn from many US TV shows alone that a guilty plea can be taken in account by a Grand Jury and they will pass their verdict accordinly, I am sure in some cases doing that can lead to a lesser punishment.
I cite TV shows as I am sure the producers have to base their storylines on actual legal laws (that isn't the right word ) as in there is little point in having a TV show set in a state with no death penalty, and have the TV show hand out a death penalty to who ever did the crime.
NYPD blue did this, when NY restored the death penalty then the detectives would remind the suspect of that fact.