Thought about this during my third play through of episode 4 (cause I want to make sure I look at everything). Even though max assumes this is from Nathan’s father (cause all of the other letters were from him) this one is obviously a note from Jefferson. Since obviously after the end of the episode we can surmise he’s the one holding the reigns in all of this.
P.S The part about Nathan screaming out his name in public obviously means it’s not Nathan’s father writing the letter. Because why would Nathan’s father care if he said his name? It’s Jefferson who doesn’t want his name called out, cause that would be suspicious.