The three devices which exploded next to Borussia Dortmund’s coach were studded with metal shrapnel and pins, one of which pierced a window and embedded itself in a head rest.
The blast, which injured a player and a policeman, had a radius of more than 100 yards and federal prosecutors said it was fortunate consequences were not more severe.
Detectives believe that only the strength of the team bus prevented the bombs causing mass casualties.
Heavy security was in place for the rescheduled Champions League match in Dortmund last night, with extra forces deployed around team hotels. Their buses took “designated safe routes” to the Signal Iduna stadium.
German police erected a large security cordon outside the stadium entrance last night after a suspicious object was found in the area. Armed police guards surrounding the cordon turned fans away and asked them to take a side path to the car park.
It was disclosed that at least two men linked to Tuesday evening’s bombing were known Isil sympathisers who had previously been on the radar of German authorities.
Prosecutors are increasingly convinced the attack was the work of an Islamist terror cell, which showed far greater levels of sophistication and planning than the recent lorry and car attacks in Stockholm and Westminster which left nine people dead and dozens more injured.
The explosive devices were hidden in a hedge close to a car park near the team’s hotel and may have been detonated by a call from a mobile phone used by someone close enough to track the coach’s movements.
The attack left Marc Bartra, the Dortmund defender, requiring surgery on a broken bone in his wrist after he was hurt by flying glass.
Yesterday afternoon he put a picture of himself on Instagram and wrote on Twitter: “As you can see I am doing much better. Thanks for all your messages. All my strength to my team-mates, fans and to @BVB for tonight.”
A police officer escorting the coach on Tuesday suffered damage to his hearing in the blast from the explosion.
Following the attack, police raided two apartments belonging to two men whom they described as “from the Islamist spectrum”. They arrested one man for questioning, a 25-year-old-Iraqi from Wuppertal. Another suspect was identified by local media as a 28-year-old German.
Police were also seeking a car with foreign-registered plates, which was seen near the scene shortly before the blasts.
The arrest came after three identical letters were found close to the scene of the attack on the bus, purporting to claim responsibility. One was said to have been left “in the name of Allah, Most Gracious, Most Merciful” and referred to the Berlin Christmas market attack in December 2016, which killed 12 people and injured 48.
It also accused Angela Merkel, the German Chancellor, of “murdering Muslims” and demanded the end of the country’s Tornado reconnaissance missions, which are part of an international coalition fighting Isil.
Frauke Koehle, lead prosecutor, said: “Two suspects from the Islamist spectrum have become the focus of our investigation.”
A spokesman for Germany’s federal prosecutor’s office added: “We found several letters of responsibility. It appears that a possible Islamist motive is indeed possible. Among other things they demand the withdrawal of [German] Tornado fighter jets from Syria and, I quote, ‘the closure of Ramstein airbase’.” Drone operations against terrorist targets in the Middle East are controlled from the Ramstein base.
The three bombs went off around 7.15pm local time in Dortmund’s Wittbraucker Strasse, as the squad was travelling to the city’s stadium for Tuesday’s Champions League quarter-final first leg against Monaco.
The explosives were detonated minutes after the Dortmund team bus had pulled away from the squad’s hotel, shattering the bus windows and scorching the side of the vehicle.
Roman Burki, Dortmund’s Swiss goalkeeper, said: “The bus turned on to the main road, when there was a huge noise – a big explosion. After the bang, we all crouched down in the bus. We did not know if more would come.”
Mrs Merkel yesterday described the bombing as an “appalling act” and praised the “wonderful show of solidarity” of football fans across Germany and in Monaco following the attack.
Dortmund lost last night’s reschedule game 3-2 to Monaco.