Two men appeared at a higher regional court in Düsseldorf on Thursday charged with committing a war crime and the membership and support of a terror organization.

The pair are suspected of having taken part in the execution of a lieutenant colonel of Syria's government forces in 2012.

What are the suspects accused of?

Investigators say the two men, aged 35 and 43, took the chained and severely abused prisoner to his execution.

One suspect acted as a guard, the DPA news agency reported, while the other one filmed and commented on the shooting in a video to be used as propaganda.

One man is charged with having belonged to a group affiliated with the Islamist al-Nusra Front terror organization.

The other is alleged to have fought for the group without being a formal member.

The two men were detained in July last year — in Naumburg in central Germany and the western city of Essen — and have been in pretrial custody since then.

The suspect accused of filming the execution pleaded not-guilty while the other man did not answer to the charges, a court spokesman told DW.

But why are they on trial in Germany?

Owing to changes to German law in 2002, it's possible to try people on charges of crimes against humanity in Germany in almost any circumstances. Neither the perpetrators nor the victims must be German nationals, the crimes can have taken place anywhere in the world.

Traditionally, the International Criminal Court would be a more standard venue for such cases — but prosecutions there often falter because many states are not full signatories to the Rome Statute. 

Last week, a former member of the Syrian secret police was sentenced to 4.5 years in prison for being an accomplice to crimes against humanity in his homeland. The ongoing trial in Koblenz is the first of its kind worldwide, and a verdict against the primary suspect is expected later this year.

Soon after the first verdict in Koblenz, Human Rights Watch sought to file charges against Saudi crown prince Mohammed Bin Salman in German courts over his suspected involvement in the death of journalist Jamal Khashoggi.