In that period, he wrote for party newspapers criticising actions taken by the HSS leader Stjepan Radić and against the Protection of State Act as unlawful.

In 1929, Jančiković led an effort to reopen investigation of deaths of Communist Party of Yugoslavia members Đuro Đaković and Nikola Hećimović in which he disproved police accounts of their killing.

)[2] After the World War II invasion of Yugoslavia, Axis puppet Independent State of Croatia (Nezavisna Država Hrvatska, NDH) was established.

The KPJ and its nominally independent branch, the Communist Party of Croatia (Komunistička partija Hrvatske, KPH) which led increasingly successful armed resistance – the Yugoslav Partisans.

Instead he wrote to the HSS leaders urging them to revive intelligence gathering and propaganda work in view of battlefield successes of the Western Allies.

Jančiković supported the idea of the HSS participating in the elections which were expected to be dominated by the KPJ due to unfair practices, but the party ultimately decided against it.

The move convinced the HSS leadership including Jančiković that the communist authorities were only interested in obtaining of legitimacy to the Croatian Republican Peasant Party (HRSS).