Reportedly, the shooter was driven by hatred for Orthodox Christians, aggravated by prolonged depression, according to Google Translate.
Additionally the article mentions that the shooter developed interest in some neo-pagan religion, "whose supporters tend to aggressive attitude to believers who profess other religious beliefs."
Here is a summer time photo of the Holy Resurrection Cathedral in Yuzhno-Sakhalinsk (from an earlier article on that site:)
Thanks for the nice picture. I have always been fascinated by Russian architecture. Isn't Islam a neo-pagan religion?
Thank you, Greysard. Lenta.ru indeed says that the motive likely is “hatred to Orthodoxy exacerbated by prolonged depression”. According to a source in the law enforcement, “a certain time ago the shooter was following a neo-pagan doctrine, the adherents to which are characterized by aggressive attitude toward believers holding different religious views. The source does not specify which particular doctrine that was. However, the source points out that the the followers of that faith have special intolerance toward Judaist, Christians and Muslim”.
Russia is now rife with sundry Wiccans under Slavic sauce, but this level of violence is so far rare.