What we don't have is any evidence ever that Alger Hiss was a spy. He was never convicted of spying. And most of the so-called evidence turned out to be bogus.
Alger Hiss lost a civil suit for defamation over Chamber's claim he was a spy, AND lost 2 perjury trials over the question as to whether he was a spy. The only reason he wasn't convicted of spying is that the statute of limitations had expired for bringing that charge.
And, as for your claim that the Soviets said Hiss wasn't one of theirs, Volkogonov left "wiggle room". "Later, the general admitted that the search had not been thorough, that it could not be complete because files had been destroyed, and that he could not speak for other intelligence agencies, just the KGB. He did not offer to check again, and the old Soviet warhorse was quoted as saying Hisss attorney had pressured him into giving his client the clearance."
AIM Report: Media Won?t Give Up on Red Spy Alger Hiss ? July B
So, obviously the issue is still not settled.