(nytimes) -- According to a statement from the federal prosecutor’s office, the Syrian — a man identified only as Mohammed G., who was arrested on Wednesday — arrived in Germany in September 2015. “Once he arrived, he acted as a contact person between the news agency Amaq, which is considered part of ISIS, and possible assailants of the terror organization,” the statement said.

If proved, the presence of a member of Amaq in Western Europe would help answer a riddle: How is it that the ISIS has continued to run a media empire, one that rapidly turns to social media to issue claims of responsibility for attacks, despite its losses of territory in Iraq and Syria?

Analysts had long suspected that the ISIS, also known as ISIS or ISIL, had media operatives on different continents and across time zones, both because of the rapid response of its statements and because its claims are frequently translated into numerous languages, including German.

“There was an assumption all along that at least a small chunk of ISIS media is run by people in the West,” said Amarnath Amarasingam, senior research fellow at the Institute for Strategic Dialogue. “This is an interesting confirmation of something people always suspected. So it’s quite important.”

Experts on terrorism first noticed Amaq in 2014, during the drawn-out battle for the town of Kobani in Syria, a prolonged confrontation that dragged out over months. They began by posting small updates on battlefield skirmishes. But they soon became the go-to outlet for the terrorist group’s claims of responsibility, posting their “bulletins” across a distinctive blue electronic backdrop, which are then uploaded to their chat rooms, or channels, on the messaging app Telegram.

It was on Amaq that ISIS first claimed a couple’s shooting rampage in San Bernardino, Calif., in 2015, and the deaths of 49 people at an Orlando, Fla., nightclub in 2016. In the last week it claimed a terrorist attack in London; a hostage-taking in Melbourne, Australia; and a pair of deadly assaults in Tehran.

The arrest in Germany could also shed light on another little-understood aspect of the news media arm of ISIS.

In most of its claims of responsibility, Amaq attributes the information to “a security source.” For example, after three ISIS followers carried out a van and knife attack in London on Saturday night, Amaq sent out this statement a little more than 24 hours later: “Security source to the Amaq Agency: A detachment of ISIS fighters carried out the London attack yesterday.”

Analysts have been puzzled by this reference to so-called sources, with many casting doubt that the terrorist group’s media operatives had any actual contacts, and suspected that Amaq was instead waiting for the mainstream new media to announce whether the assailant was Muslim.

The statement from the prosecutor explains that Mohammad G. had been communicating via social media with a man who went on to carry out a 2016 arson in Sweden.

Mohammad G. contacted his source after the attack to confirm details of what had happened, according to the statement. “One day after this attack, the accused demanded from his contact person (in Sweden) a personal claim of this deed,” the prosecutor’s office said. “The background was that Amaq did not want to issue a report about the attack without such a claim.”

The statement continued: “After that, IS claimed the attack in the al-Naba newspaper which it publishes,” referring to the group’s weekly newsletter, which occasionally claims attacks ahead of Amaq.

The attack in question occurred in October 2016 in Malmo, Sweden, when a 30-year-old Syrian man threw a Molotov cocktail at a community center.

According to an English-language news organization, The Local, investigators found an image of the ISIS flag, videos showing ISIS members killing people and instructions on how to make a detonator on the man’s computer. The events led to a debate, with one district court judge initially dismissing the violence as arson and not terrorism. Many in Sweden and beyond used social media to say that ISIS’s assertion of responsibility showed that “they claim anything.”

In fact, the German statement gives an indication of the fact-checking process that was carried out in at least one case before ISIS makes a claim.

“We’ve all assumed that they are reading news reports, and then saying, ‘Our guy did this.’ But this is interesting because this does show that they clearly have someone, who is one of their guys, and who is getting verification and confirming that this attack was in our name,” said Shiraz Maher, the deputy director of the International Center for the Study of Radicalization at King’s College, London, cautioning that the news release mentioned only a single example.

Despite a widespread view that the ISIS opportunistically claims attacks with which it has little genuine connection, its track record — minus a handful of exceptions — suggests a more rigorous protocol.

At times, the ISIS has gotten details wrong, or inflated casualty figures, but the gist of its claims is typically correct. The group has made it clear that it considers itself responsible both for acts carried out by its own personnel, as well as acts carried out by people who lack direct ties to the group but were inspired by its propaganda.

In several instances, moreover, the ISIS has claimed attacks before the identities of the killers were known.

For example, it was not until Monday evening — one day after ISIS claimed the London attack — that police identified two of the three attackers, and it was only on Tuesday that the name emerged of the third attacker, who had been stopped at an Italian airport in possession of ISIS propaganda.

Similarly, Amaq claimed the shooting in the Orlando nightclub before police released the transcript of the 911 tape, which showed that the gunman, Omar Mateen, had repeatedly told the phone dispatcher and later a police negotiator that he was carrying out the violence in the name of the ISIS.

“Much like with any media, or journalist, they thrive on credibility,” said Mr. Amarasingam. “It doesn’t make any sense that they would just go out and claim every garbage can that gets kicked over. It doesn’t work that way.”