Until this morning, investigators in Germany had remained tight-lipped about the motive behind the targeted triple-bombing of a soccer team yesterday, which seriously injured one player. The takeover of the probe by prosecutors suggested that terrorism had become the focus of the probe. This morning, prosecutors made an arrest after conducting a search of the home of a suspect with “Islamist links,” according to the BBC:

German police have detained a suspect with “Islamist links” following a bomb attack on the bus of the Borussia Dortmund football team. …

Lead prosecutor Frauke Koehle said: “Two suspects from the Islamist spectrum have become the focus of our investigation. Both of their apartments were searched, and one of the two has been detained.”

Reuters also confirms the arrest, and that a second arrest may still come:

A man of Islamist background has been detained by German investigators probing blasts against a bus carrying players of Borussia Dortmund soccer club, the federal public prosecutor’s office said on Wednesday.

It said investigators had searched the apartments of two suspects from Germany’s Islamist scene and decided to detain one of them.

It did not say where the suspect was detained but added that a decision would be made on whether to seek a judicial arrest warrant against him.

The Telegraph has a live blog running on the investigation, and has more on the letter left behind at the attack. The letter makes the motive clear, which is likely why prosecutors took over the investigation so quickly:

German investigators are examining a possible Islamist link to three explosions that rocked the Borussia Dortmund football team bus after a letter found at the scene “in the name of Allah” reportedly referred to the Berlin Christmas market attack.

The letter also named Angela Merkel and mentioned Germany’s deployment of Tornado reconnaissance missions as part of an international coalition battling Islamic State of Iraq and the Levant (Isil), according to local media.

Three explosions occurred as the Dortmund squad were travelling to the Signal Iduna Park stadium for Tuesday’s Champions League quarter-final first leg.

According to German media, a letter found near the scene referred to 2016’s attack on a Berlin market and began: “In the Name of Allah, Most Gracious, Most Merciful.”

According to the Telegraph, a second letter was found that implicated anti-fascist activists. Prosecutors have pursued both angles, but according to the Telegraph, they now think the second letter is a fake. They were somewhat skeptical of the first letter too, but news of the arrest makes it seem as though they have begun to corroborate it. That letter declares the bombing to be a follow-up to the Berlin Christmas attack, and that athletes from “Crusader nations” are on ISIS death lists:

The letter refers to the attack on the Berlin Christmas market and claims that German forces are involved in the killing of Muslims in the Islamic State’s caliphate.

Athletes and celebrities in “Germany and other crusader nations” are therefore on a “death list of the Islamic State,” the unsigned, typed letter claims. Dpa reports it also mentions German Chancellor Angela Merkel by name.

The letter also demanded the withdrawal of German planes from Turkey and the closure of the US airbase at Ramstein. However …

The dpa is reporting that both letters could be fakes as neither bear the hallmarks usually associated with either group, and further checks are needed.

So what do we know? For one thing, we know the athletes were fortunate not to have been killed:

A spokesman for the Bundeskriminalamt also revealed that they were fortunate to not be dealing with any casualties after shrapnel was found lodged in other areas of the bus.

“These explosives contained metal shards – we can be happy that nothing worse happened. One of the metal shards in the explosive remained lodged in a seat headrest. It could have been worse.”

Bear in mind, of course, that these are still early days in the investigation, and that arrests do not necessarily determine guilt or truth. From the brief description of these arrests across a number of media outlets, it’s not clear whether the arrest is firm or merely a procedural detention while investigators collect evidence. The investigation could take a different turn, and the real perpetrators might have entirely different motives (or the same motives with different perpetrators). For now, though, this does look like a continuum of smaller-scale attacks on European soft targets especially focused on entertainment and travel.