Police secure the stadium before a match between Borussia Dortmund and AS Monaco in Dortmund, Germany, on April 12. (Sascha Steinbach/European Pressphoto Agency)

German prosecutors requested an arrest warrant Thursday for a 26-year-old Iraqi national with suspected links to the Islamic State group who is being held in connection with a bomb attack on a popular soccer team.

The statement said there was no direct proof yet that he was involved in Tuesday’s attack on the bus of the Borussia Dortmund team that left one player injured, but there is evidence he was the leader of a 10-man Islamic State unit in Iraq involved in killings, kidnapping and blackmail.

He left Iraq in March 2015 for Turkey before heading on to Germany in early 2016 and has maintained his contacts with the extremist Islamic State group, the statement continued.

Three explosions went off around 7 p.m. near the bus carrying the Borussia Dortmund players as it was on its way to a home match against AS Monaco in the Champions League.

The match was later rescheduled. Dortmund lost, 2-3.

Three identically worded letters were found at the scene demanding the withdrawal of the German Tornado jets supporting the fight against the Islamic State in Syria and the closure of the U.S. air base in the German town of Ramstein-Miesenbach.

Speaking at a news conference in Berlin Wednesday, Interior Ministry spokesman Tobias Plate called the use of letters “atypical” compared to previous terror incidents in Germany, which focused on doing harm to random individuals.

If the attack had an Islamist motivation, it would be a new twist to the terror incidents in Germany, focusing on specific institutions or celebrities, rather than just bystanders, such as the truck that plowed into a Christmas market in Berlin last December.