Kammala wannan jumla: Kosonen ya yanke shawarar komawa Finland a 1905. Ya shiga cikin ayyukan Jam'iyyar Social Democratic, kuma ya yi aiki a matsayin editan jaridar "Kansan Lehti". A lokacin juyin juya halin Rasha na 1905, Kosonen ya shirya mafaka ga 'yan gudun hijira daga yankin Baltic na Daular Rasha, ya kuma taimaka wajen shirya
Disamba 1905 Taron Bolshevik na Tampere. A watan Fabrairun 1906, ya taimaka wa ɗan juyin juya halin Latvia Jānis Čoke, wanda daga baya aka bayyana cewa ya shiga cikin fashin reshen Bankin Gwamnatin Rasha a Helsinki.