My understanding of the issue is that, when the bodies were first discovered by the Nazis during the invasion of Russia, the Soviet government maintained no Polish officers were murdered in Katyn in 1940 and that it was the later work of the Germans.
Your posting of the short article seems to imply that the case was dismissed by the Moscow municipal court due to a report by the Russian prosecutors there were no records on the event in Russian military archives. How convenient - for Russia.
Is filing the complaint in Russia, having it dismissed, then taking it to the European Court of Justice all part of a single strategy for bringing Russia into an international legal forum and making it admit to the role the previous Soviet government played in the the killings?
The use of the term rehabilitation is also interesting. Is it the case that the Soviets later maintained that the Poles were criminals that were executed? (Hence the need for rehabilitation.)