The first trial in Germany for war crimes in Syria began Tuesday against a 21-year-old who allegedly posted photographs of himself posing with two severed heads, Agence France-Presse reported. The case is one among almost a dozen cases authorities are investigating related to alleged atrocities in Syria or Iraq, in addition to more than 30 cases of individuals who are suspected to have belonged to extremist groups.

Aria Ladjedvardi, a German national of Iranian descent, is accused of having posed alongside the severed heads with two fellow fighters in a move prosecutors allege was intended to belittle their victims. Ladjedvardi was arrested in October last year in Frankfurt following a police raid on his apartment and has been in police custody ever since.

He reportedly traveled to Syria in early 2014 in order to join the battle against Syrian leader Bashar Assad. The pictures with the severed heads were posted on his personal Facebook page. Prosecutors say Ledjedvardi also received weapons training in Syria.

It was not immediately clear what extremist group Ladjedvardi allegedly belonged to. There are various groups designated as terrorist organizations operating on the ground, including, most notably, the Islamic State group and the al Qaeda-affiliated Nusra Front.

Some 600 individuals have traveled from Germany to fight in Syria. That makes Germany a significant source of foreign fighters in Syria and Iraq; neighboring France has seen some 1,600 people leave for Syria. Western governments have struggled to track individuals who have returned home from the battlefield, and prosecutions have been sparse.

Many countries fear returning fighters could pose a danger to their home countries. The issue has been of heightened concern since returning fighters took part in terrorist attacks in Paris last November, killing 130 people, and then again in Brussels this year, killing more than 30.