Almost a week after the attack on a bus carrying the German football team Borussia Dortmund, police have said they are continuing to investigate “in all directions” and have questioned the authenticity of three separate statements that claimed responsibility for the attack.

Copies of a statement suggesting an Islamist motive were found near the site where three explosive devices were detonated last Tuesday, and a 26-year-old Iraqi who had previously led an Isis unit was subsequently arrested.

But police have since been unable to link the suspect directly to the attack, and terrorism experts have cast doubt over the language used in the statement, suggesting it could have been faked to pin the attack on radical Islamists.



A second statement – purportedly by an anti-fascist group critical of Borussia Dortmund for failing to do enough against rightwing extremism – was uploaded on the leftwing website Indymedia on the night of the attack but was quickly dismissed as a fake by officials.

On Thursday, a third statement was emailed to the Berlin newspaper Tagesspiegel. The anonymous author cited Adolf Hitler and railed against multiculturalism. On Saturday Germany’s Federal Office of Criminal Investigations said it “rather ruled out” the possibility that the author of the email had also written the statement found near the crime scene.

Borussia Dortmund’s management has in recent weeks distanced itself from a far-right contingent of supporters, some of whom had attacked fans of RB Leipzig, including children, when the two sides met in February. Graffiti containing a death threat against the Dortmund chief executive, Hans-Joachim Watzke, signed by the fan group “0231 Riot” was discovered in the city days after the incident.

Dortmund players hold up the No 5 shirt of Marc Bartra on Saturday. Bartra was seriously injured in the 11 April attack. Photograph: Ina Fassbender/AP

“It is widely known that Dortmund suffers from a rightwing extremist scene,” Sebastian Fiedler, the head of the Association of German Criminal Investigators, told Die Welt newspaper on Sunday. “Clues leading investigations into that direction will therefore have to be followed up too”.

On Monday police sought to quash rumours that investigations had pinpointed a single motive, telling the German news agency dpa that “the pendulum swings neither in the direction of rightwing extremism or Islamism”.

Other groups with a possible motive cited in German media reports include criminal betting syndicates or a foreign intelligence service trying to destabilise the political climate before federal elections in September.

While police on Monday would not confirm media reports speculating that the explosives may have been sourced from the German army, officials told dpa that the explosives used could not have been obtained easily.

As more details of the attack have emerged, it has become apparent that Borussia Dortmund’s players came closer to death than had previously been thought. Most of the metal pins in the explosive device flew over the top of the bus, only one of them embedding itself in a neck rest inside the vehicle.

“If the bombs had been fired around one second earlier, the bus would have taken the full load,” an investigator told the Bild am Sonntag newspaper. “Then there would have certainly been several severely injured and maybe even dead people.”