Hugh McInnish, who knew Jeff Sessions when he was AG of Alabama makes no mention of Sessions being nicknamed back then, the Silent Executioner.
I'm still looking for proof that he was called that. Do you have any?
No, I did not find any evidence of Jeff Sessions being called “the Silent Executioner” from back around the time that he was the US Attorney who took down the Democratic Party’s terrorist arm at the time, the Ku Klux Klan in Alabama.
It seems to be a more modern nickname.
The underlying facts of his quiet and effective prosecution - that he got the only death penalty of the 20th Century for a Klansman (Henry Hays) convicted of killing a Black (Michael Donald), and that Sessions himself later got the sentence carried out as State AG, are public record beyond dispute.