[3] Karu dabbled in filmmaking, and directed, wrote, edited and produced the comedy short films Ylioppilas Pöllövaaran kihlaus and Sotagulashi Kaiun häiritty kesäloma for Suomen Biografi Oy, both of which were released in 1920.

[8][9] Throughout the rest of the decade and the early 1930s, Karu continued to direct popular films, such as Myrskyluodon kalastaja (1924), Suvinen satu (1925), Muurmanin pakolaiset (1927) and Nuori luotsi (1928).

[10] Suomi-Filmi ran into financial difficulties after the global depression stemming from the Wall Street crash of 1929 caused the attendance figures of cinemas to drop.

[12] After leaving Suomi-Filmi, Karu wasted no time, and only months later started what would become his old company's main rival, Suomen Filmiteollisuus.

[14] Karu held the title of head director in his new company, but during his short stay there could only direct two films, Syntipukki and Roinilan talossa, both in 1935, neither of which was very successful.