There are many things suspicious about it, but right now, let's hone in on one: The letter states that FBI Agent Hosty visited "us" in Dallas on November 1, 1963. But, Hosty visited only Marina and Ruth Paine in Irving on November 1, and Oswald wasn't there. Oswald and Hosty did not meet, face to face, until November 22, 1963 at Oswald's first interrogation. The letter states that on November 1, "Hosty warned me" that if I engage in FPCC activities in Dallas that the FBI will again become interested in me.
So, how did Hosty warn Oswald? It wasn't face to face. And it wasn't on the phone either because there is no claim that they ever spoke on the phone.
If you read the letter, it implies that Oswald was present at the meeting in Irving, but he wasn't. He wrote that he and his wife strongly protested, etc. The clear implication is that he, Oswald, was there.
Why would Oswald lie about that? Wasn't it just as easy to be truthful, to say that the meeting was between Hosty and his wife, and that he only heard about it later from her? Why would he lie?
And, the misspellings in the letter are over the top. They are beyond credibility. "Of cores" for "Of course" is ridiculous. Oswald supposedly taught himself Russian and could speak, write, and read in Russian. George DeMohrenschildt said that Oswald could read the Russian classics in Russian. And yet, he couldn't spell "of course", one of the most common and frequently used expressions in the English language?
In a letter to the Soviet embassy, he misspelled Soviet Union, spelling it "Uion"?
So, he lived there for 3 years and tried to defect there, but he couldn't spell it?
He spelled "comrade" correctly, even though phonetically it's pronounced "comrad" and yet he typed "Soviet Uion" and "Of cores"? Then, subsequently, he misspelled it "of couse"? We are supposed to believe all that?
Even if Oswald was as bad at spelling as they claim, which I doubt, when typing important letters, don't you think he would be careful? He was asking them for something, so why would he mistype the name of their country?
This is just part of the whole depiction of Oswald as deranged, eccentric, scatterbrained, and mired in incompetence and confusion- that he was off his rocker. I don't believe for one second that he sent that letter.