The whole "blur" surrounding the clash between the SBU and the GUR is "slowly lifting", though it remains shrouded with a significant amount of "uncertainty" and, frankly, as the story goes on it looks and sounds more and more like the scenario of a bad action movie.
At the onset, aside from the rivalries between the SBU and the GUR, rumors circulated about the FSB being involved in some way shape or form, and also members of the RDK.
A version was the FSB had tried to abduct the leader, or one of the leaders, of the RDK, prompting the SBU and GUR to show up. However the "FSB" part of the claim seems to vanish for some reasons, and a firefight between the SBU and GUR still ends up breaking out.
What happened to the FSB? We don't know.
Why did the SBU and GUR started shooting at one another? We don't know. Or rather, the official version is the usual sanitized eastern-Europe phraseology: an "urgent investigative actions" during which "an unacceptable conflict situation arose, which led to the shooting."
What happened to the RDK, its leader or leaders? Apparently only one member of the RDK was involved and got "rescued".
Now, it appears the SBU has officially accused the leader of the RDK of working for the FSB. The SBU supports these accusations by having released screenshots of mails and text-messages exchanges, as well as a video confession from the RDK deputy commander.
According to the confession obtained by the SBU, Kaplunov was supposed to conduct the assassination of a "leader of the Russian opposition" who was planning on visiting Ukraine for Independence Day.
According to the SBU, Kaplunov admitted to contacts with the FSB and helped identify those in the conspiracy. The SBU claims that he cooperated voluntarily, thus providing a reason as to why he was not taken into custody.
However, Kaplunov stated that he was held for several days, confessed to contacts under duress and was detained in secret for about nine days. He also denies the existence of any no such contacts as alleged by the SBU. Kaplunov explains rescue by "comrades" from the GUR which eventually triggered a firefight between the GUR and SBU.
As of now, at least, that's the story so far. Maybe it is the "official one" to be, or maybe there will be another version or further develoments.
A "Mommy and daddy are fighting and we don't know why." kind of mess.