Police officers probing the attack on a priest in the quiet northern French town of Saint-Etienne-du-Rouvray were led to an unusual location in their investigation: Telegram, a messaging application that has 100 million active users worldwide.

With both private and public chats, the application's flexibility, as well as its policy on privacy, makes it attractive to users, especially those in countries with repressive political regimes. About 15 billion messages are sent on the application every day.

Adel Kermiche and Abdel Malik Petitjean, the two French ISIS jihadists who killed the priest, appeared to have used Telegram before they carried out their attack.

"The investigation that has just begun is interesting because it addresses two key notions of jihad: the narcissistic and personalized aspect of a crime and the duality between terrorism and mass communication," said an investigating officer.

"Share it ASAP"

The Anti-Terrorist Division of Judicial Police (SDAT) found that Kermiche and Petitjean met for the first time on Telegram on July 22. The following day, they met in person. Petitjean, who lived in Savoie in southeastern France, came to see Kermiche, who was under judicial review in Saint-Etienne-du-Rouvray, just days before the attack.

The two terrorists shared their plan with others. Petitjean told his cousin Farid K what he intended to do. (Farid K has since been slapped with terror charges.) Kermiche posted boastful audio messages on Telegram to a group of more than 200 users. "You take a knife, you go to a church and you create carnage. You cut off two or three heads and it's good, you're done," he said, encouraging other users to take part in the process. "I'll let you know a couple of minutes before I start and, when it happens, you should share it ASAP."

The police officers are working on the networks of people the two terrorists knew. The duo, especially Kermiche, may have been influenced by a foreign preacher. The two militants were shot dead by police shortly after they killed the priest.

Everything a potential jihadist needs

It's no coincidence that terror group ISIS has chosen Telegram as one of their communication tools. The application has the functionality of both social networks and encrypted messaging systems like WhatsApp and Signal. Users can send single recipient messages or hold private group discussions.

Jihadists want to address a small community online, not reach out to the kind of large audiences that Facebook and Twitter have, explained Romain Caillet, a French jihad expert. "Their main goal is to keep their supporters informed. Telegram is very helpful to keep it all between jihadists. Some of them seek to relay information while others are meant to receive it," he said.

Abdel Malick Petitjean Photo: Wikimedia Commons

On Aug. 1, 2016, the propaganda outlet for ISIS, Amaq Agency, created a new broadcast channel on Telegram. Minutes later, the first dispatch appeared. "Breaking. A second martyrdom operation took place yesterday. A vehicle carrying a bomb hit Iraqi forces near Qayyarah in Niniveh."

The message was followed by another about a missile attack in Manbij, Syria. In total, seven messages were posted in seven minutes on the channel. More than 200 people began to follow the channel. Other channels describing themselves as "authentic broadcast media" popped up on Telegram.

One of them called "Fighting Journalists" shares English-language propaganda — from reports of attacks and photos of the Syrian civil war to maps of areas occupied by jihadists and links that direct to videos of preachers calling for armed combat. In short, everything one needs to become a jihadist.

Fighting Journalists has 600 followers and only the administrator has access to the usernames of members.

Often, channels vanish shortly after they appear. While some aren't updated for weeks, others are deleted and recreated under new names to avoid detection. That's what happened to the Amaq Agency channel, which could not be found a day after it was launched.

"Media uproar"

Messaging services have become crucial for intelligence services. In addition to Telegram, authorities are examining other applications like WhatsApp, Signal, Viber and IMO but it's easy to get lost in the maze of fake accounts and usernames, sometimes used by the same person as a cover.

"We then proceed to directly interview close relatives," a police commander said. "When they worry about the radicalization of a specific member of the family they might cooperate by providing the right accounts and passwords."

Although ISIS finds Telegram useful, it does not revolutionize the way attacks are carried out, one analyst argued.

"Apart from the crime, what matters when it comes to a terrorist attack is that it causes globalized communication. Jihad has always enriched itself with media uproar and now there is no longer a need to conduct an operation as spectacular as 9/11 to make headlines worldwide. With social networks, a tweet claiming responsibility for the killing of someone is sufficient to make the world go crazy," said political specialist Abdelasiem Em Difraoui.

Still, the application is a thriving medium for ISIS propaganda. For Caillet, the French researcher specializing in jihad, Telegram is the logical successor to Facebook and Twitter — platforms where administrators have increased censorship of ISIS propaganda in recent years.

"It will take one or two other attacks before Telegram will do the same," Caillet said. After the November 2015 Paris attacks, Telegram's administrators closed 78 accounts linked to ISIS. No doubt more will be shuttered in the future.