Rubuta ci gaba don wannan sakin layi - 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 taron bolshevik na Tampere a watan Disamba na 1905
Ka yi haƙuri. 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.