An Iraqi national arrested over the bomb attack on the Borussia Dortmund team bus is a suspected member of the Islamic State group, according to German prosecutors.
But prosecutors say they have so far found no evidence to link the 26-year-old, whom they allege led a 10-strong unit which prepared abductions, extortions and killings in Iraq, to Tuesday night's attack.
They have requested an arrest warrant to be able to hold the man, named only as Abdul Beset A, over his Islamic State links. They say he travelled to Turkey in March 2015 and Germany early the following year.
The attack forced the postponement of Dortmund's Champions League match with Monaco and left the club's defender Marc Bartra needing surgery on an arm injury.
A statement from the German Federal Prosecutor's Office said: "The accused is strongly suspected of being involved in Iraq as a member of the foreign terrorist group 'Islamic State' (IS).
"The accused was arrested (on Wednesday) in connection with the attack on the Borussia Dortmund team coach. The investigations have so far shown no evidence that the accused participated in the attack.
"However, the accused is suspected of joining Islamic State at the latest by the end of 2014 in Iraq.
"According to our intelligence, he was in command of a unit of about 10 people. The job of his unit was to prepare abductions, extortions and also killings.
"He is also said to have fought for unification. In March 2015 he travelled to Turkey and from there to Germany in early 2016. From Germany the accused continued to maintain contacts with members of 'IS'."
Prosecutors say a judge will decide on Thursday whether the man can be held for further investigations.
Dortmund lost the rearranged quarter-final first leg 3-2 to Monaco on Wednesday night, less than 24 hours after three explosions went off near the bus as it travelled to Signal Iduna Park for the original game.
The explosives contained metal pins, one of which was found embedded in one of the headrests on the bus.
Prosecutors revealed on Wednesday that three similar letters claiming responsibility were found near the site of the attack which indicated an Islamic extremist background.
The letters called for, among other things, the withdrawal of Tornados from Syria and the closure of the Ramstein Air Base.