Why is this case being tried in a military court?

Russia's Moscow Garrison Military Court is trying a retired Ministry of Internal Affairs general officer for extortion. Why not a civilian court? Details here, from CrimeRussia. Excerpt:

Police Major-General Viktor Trutnev left law enforcement agencies seven years ago. He was appointed Head of the Moscow Criminal Intelligence in 2001. Two years later, he was appointed Head of the Department of Internal Affairs of the North-Eastern Administrative District of Moscow. After being transferred to the Department of Internal Affairs of the Northern Administrative District in 2011, Trutnev had to retire after several months. The reason for it was a scandalous incident when Head of the Ministry of Internal Affairs, Rashid Nurgaliev, visited the Academy of the Interior Ministry located on the territory of the Northern Administrative District of Moscow. When approaching the Academy, the honored guest saw a rude inscription on the ground that said ‘Nurgaliev is a ***hole.’ After that, Trutnev was hospitalized with a heart attack, and a few months later, Dmitry Medvedev signed a decree on his resignation.