Erik is engaged in PhD research on the concept of and rule on complicity in the international law of state responsibility.
He teaches in the Bachelor course on international law and is involved as an associate editor for the International Law in Domestic Courts programme. Both to this programme and the Annoted Leading Cases International Criminal Law book series (eds. Klip/Sluiter) he contributes as an author. His study of the legal status of members of armed groups in non-international armed conflicts was awarded the 2006-2007 prize for Best Thesis of the Leiden University Law Faculty. He is also employed in a defence team before the United Nations International Criminal Tribunal for the Former Yugoslavia.
His research interests include the international law of state responsibility, international humanitarian law, international criminal law and legal theory.