I believe it does already, atleast to a certain degree. You can agree not to press charges against an individual. I think it depends on teh severity of the offence though.

Murder is considered a crime not only against the individual, but against the society as well. So, the DA looks out for the common good. I think that's why you'd not see something like what happened in Saudi Arabia happen in the US.

Besides, I would guess that prince basically paid his way out of prison. He paid off the family so they'd agree to the reprieve.