A trial relating to a 2016 murder of a priest began in Paris on Monday.
The attack that resulted in the death of 85-year-old priest Jacques Hamel in a Catholic church in Saint-Etienne-du-Rouvray near Rouen shook France.
Police shot and killed the two assailants on the scene. The trial involves alleged accomplices.
Who is on trial?
French authorities initially charged four men, including the alleged instigator, for the attack. However, the alleged instigator is believed to have died in a bomb attack in Iraq. As his death is not officially confirmed, he is on trial in absentia.
The other three face charges of membership in a terrorist organization, which they have denied. Their lawyers have described them as "scapegoats."
The two attackers, both 19 and who were shot and killed on the scene, had claimed in a video to be members of the so-called "Islamic State" (IS) group.
IS later called them its "soldiers" and said the attack was in retaliation for France's fight against jihadis in Syria and Iraq.
Prosecutors have said the three knew about the attackers' plan, and one of them had accompanied one of the attackers to Turkey — in an attempt to reach Syria — just weeks before the murder.
During morning Mass on July 26, 2016, two attackers first took six people hostage in the church in a working class suburb.
Hamel had his throat slit at the foot of the altar, but a nun was able to escape and raise the alarm.
One of the worshipers taken hostage, Guy Coponet, was also seriously injured. Coponet, now 92, is expected to attend at least part of the court sessions "to understand how these youths, barely out of adolescence, could commit such horrors," his lawyer told the AFP news agency.
France has faced a series of jihadi attacks that began with the 2015 Charlie Hebdo massacre.
fb/dj (AFP, dpa)