Together with judges Hans-Peter Kaul and Ekaterina Trendafilova, Tarfusser made the landmark decision that saw Kenyan President Uhuru Kenyatta, his Deputy William Ruto, former Head of Civil Service Francis Muthaura and journalist Joshua Sang committed to trial in January 2012.

[4] In February 2015, Tarfusser and Trendafilova dissented with their colleagues of the Pre-Trial Chamber II in their decision to uphold the acquittal of militia leader Mathieu Ngudjolo Chui of commanding fighters who destroyed the village of Bogoro in eastern Congo in 2003, raping and hacking to death some 200 people including children.

"[5] In March 2015, Tarfusser unsuccessfully ran for the office of President of the International Criminal Court; he ended up losing to Silvia Fernández de Gurmendi by one vote.

As presiding judge of the Pre Trial Chamber II, Tarfusser was also put in charge of the case against LRA leaders Joseph Kony, Vincent Otti and Okot Odhiambo.

[9] After September 2015, Tarfusser served as presiding judge in the case of Ahmad al-Faqi, the first individual to face charges of the war crime of damaging mankind's cultural heritage at the court.