The KGB was an intelligence and security agency. Unless these were fronts, intelligence agents don't work as teachers, tour guides, or as engineers in nuclear plants.
The equivalent would be the CIA and the NSA in the US.
Maybe Zolotaryov was a retired KGB agent. Even if Krivo was an agent, he must have been in a junior rank and that means little access to sensitive information. But maybe he wasn't an agent but an engineer at a nuclear plant and had some inside information...
Someone wanted that information so bad that they mounted an operation to infiltrate Russia, track down the hikers who didn't even share the route plan with the university, torture Krivo to extract that information and then murder everyone, all the while leaving no trace.
This must have been a foreign intelligence agency, most likely from the US.But the thing is, if this was a CIA operation to gain information about the Mayak plant, or even if there was a slight suggestion that was the case, the Soviet Union wouldn't need to cover anything up and would openly blame the US.
It would be in their own domestic and also international diplomatic interests to investigate and reveal the full truth about this evil foreign power murdering 7 or 8 civilians only to get information from a KGB agent.
But if it was a CIA operation, all of this would be unnecessary. They could monitor the group with night vision goggles at night for example, wait for Krivo to emerge alone to relieve himself, and capture him without harming the others. And detain him long term either taking him abroad or in some secreted undetected CIA facility within Russia to get the most amount of information out of him because usually people take time to start talking...
Because of all of this, I think this is very unlikely. If Krivo was tortured, it wasn't because he was a KGB agent or had information about Mayak.
And that is IF
he was tortured. I would like to remind about light hearted photos of Rustem posing in Krivo's burnt quilted jacket which seem to be from the day before the incident: https://dyatlovpass.com/camera-krivonischenko
So it's possible he burning himself is completely unrelated to and predated the incident.