Three explosions that went off near the bus carrying the Borussia Dortmund football team in Hochsten, about 10 kilometers from the Westfalenstadion, could also have been the work of far-left Antifa militants.

Dortmund

Investigators examined two different letters claiming responsibility for the explosions – one found near the scene which used an Islamist introduction, and another connected to far-left extremists.

The team bus was not severely damaged in the blast, which police are also treating as a possible jihadist attack “based on the facts of the crime”. But according to DPA sources, police were investigating a second letter claiming responsibility for the attack on a bus ahead of the Champions League game against Monaco.

The letter was found on Tuesday online, reportedly saying that the attack was against the team because of Borussia Dortmund symbolises “racism, Nazis, and right-wing populism”.

On the left-radical platform “linksunten.indymedia.org” it was stated: “Today we attacked BVB’s bus with specially designed explosives.”

The contribution was posted online shortly before midnight but is no longer available, as the site owners had it deleted. On Twitter, however, screenshots of the post had been saved.

It appears to be the first time that jihadist militants had joined forces with left-wing extremists. After the attack on BVB’s teambus, German security expert Malte Roschinski told Quelle24 the attack was not typical. “This whole approach is very untypical for ISIS.”

Roschinski also said that the three explosive devices were most certainly the work of professionals and he suspects that the bombs must have been detonated by someone who had been near the site of the explosion. He did not rule out that ISIS could have enlisted the services of other parties to make the attack possible.

A spokesperson for the public prosecutor, Frauke Koehler, said shrapnel from the explosive devices used in the attack contained metal pins which had pierced a headrest of a bus seat and had traveled more than 100 metres.

German police maintain that the exact motive remains unclear. According to a police statement on Wednesday one suspected Islamist had been detained after the explosive attack against the Borussia Dortmund team on Tuesday.

They had questioned two Islamist suspects – one of whom was detained – and stated that there is a possible “terrorist link”. DPA cites unnamed sources who say the suspect detained was a 25-year-old man from Iraq, while the other suspect who was not detained is reportedly a 28-year-old German from Fröndenberg.

According to local newspapers Kölner Stadt-Anzeiger and Express, both are suspected of being close to terror group ISIS.

Player Marc Bartra was injured with a broken wrist bone, while a police officer was also hurt amid the blasts.