Norman Mailer said he was given access to some Belarus KGB files shortly after the collapse of the Soviet Union but that they were less extensive than he hoped. Still he said he was able to interview some two dozen KGB agents including the ones that monitored Oswald and his conclusion was there's nothing there. Oswald was viewed as an oddball and they were happy to see him return to the US and not potentially cause an international incident. Many of the agents were around during the Stalin era and they learned firsthand to not draw attention to yourself. They were worried that Oswald would do that.
From Mailer's "Oswald's Tale".

Dear Steve M.,
When one reads Masha Gessen's 2012 book,
The Man Without a Face: The Unlikely Rise of Vladimir Putin, one realizes that in August of 1991 the KGB orchestrated a planned-to-fail "hardliner coup" so that power could be transferred from Gorbachev to Yeltsin with the unspoken understanding that Yeltsin was forever beholden to it and that it was still in control of everything.
Bottom line: Why would anyone believe what a bunch of current or "former" KGB officers said in the former USSR about the KGB's alleged non-involvement with a former Marine sharpshooter and U-2 radar operator during the two-and-one-half years he lived half-a-mile from a KGB school in Minsk, married a probable KGB informant (according to true defector Pyotr Deriabin) and then returned to the U.S. and 1) attempted to assassinate General Walker, 2) did assassinate JFK, and 3) murdered DPD officer Tippit?
All of which reminds me of KGB Colonel Oleg Nechiporenko's 1993 book,
Passport to Assassination, in which he implausibly devotes fifty pages to extolling the alleged bona fides Yuri Nosenko and condemning the paranoiac, incompetent, and sadistic natures of his anti-Nosenko / pro-Golitsyn primary case officer, Tennent H. Bagley, and Bagley's anti-Nosenko / pro-Golitsyn colleagues.
And how, on 11/22/93, then-KGB General Nikolai Leonov (RIP; aka "The Blond Oswald in Mexico City), without mentioning Oswald's alleged weeping and revolver-brandishing meeting with Nechiporenko, Yatskov and Kostikov at the Consulate on Saturday, 9/28/63, told National Enquirer that Oswald interdicted him during volleyball warmups on SUNDAY, 9/29/63, and started ... yep ... weeping and brandishing his revolver in his Embassy office .
LOL!
-- Tom
PS Here's Bagley's free-to-read 2007 book,
Spy Wars: Moles, Mysteries, and Deadly Games.
https://archive.org/details/SpyWarsMolesMysteriesAndDeadlyGames