The announcement marked a setback for investigators, who have called the three blasts late Tuesday a "terrorist" attack.
The announcement marked a setback for investigators, who have called the three blasts late Tuesday a "terrorist" attack and said they are focusing on suspects in the "Islamist spectrum".
"The investigation has not found evidence that the suspect took part in the attack," the federal prosecutor's office said in a brief statement.
It said it was nevertheless seeking an arrest warrant for the 26-year-old Iraqi national, identified only as Abdul Beset A., for alleged ties to the Islamic State group.
Investigators had zeroed in on two suspects believed to belong to the large jihadist scene in the Ruhr Valley, after three identical letters claiming responsibility for the attack were found at the scene.
The letter demanded that Germany withdraw its deployment of Tornado reconnaissance missions in the anti-IS international coalition and close the US air base in the western German town of Ramstein.
The daily Bild said that police had had Abdul Beset A. under surveillance for several months and believed, based on tapped telephone conversations, that he might be hiding explosives in his flat.
However a raid on his home Wednesday turned up blank, the report said, adding that investigators were still pursuing leads to the attack in the extreme right and far-left scenes.
Even as the probe seemed appeared to be in the preliminary stages, Dortmund officials criticised the decision to play its postponed Champions League match just 24 hours after the attack, with the perpetrators still at large.
The roadside blasts left Dortmund's Spanish international Marc Bartra and a policeman injured, with the bombs "containing metal pieces" detonating minutes after the team bus set off to a planned Champions League game against Monaco on Tuesday night.
The quarter-final, first leg match was held in the western German city 24 hours later, with Monaco claiming a 3-2 win.
Borussia Dortmund coach Thomas Tuchel angrily accused UEFA of treating the bomb attack on their team bus as if a "beer can" had been thrown and claimed they were informed by text message that they would have to play their Champions League game.
Former German international Lothar Matthaeus said it was "irresponsible" to get the players to go through with the game so soon after the attack.
"From what I heard from team sources, many players didn't want to play today. But UEFA put on pressure and politicians urged Borussia Dortmund to counter terror," he told Sky news channel, referring to the European football federation.
Chancellor Angela Merkel said Wednesday she was "horrified" by the "repugnant act", which Dortmund city's police chief Gregor Lange described as a "targeted attack" against the team, also known as BVB.
Germany has been on high alert since a series of jihadist attacks last year, including a Christmas market truck rampage in Berlin.
Tuesday's explosives detonated minutes after the Dortmund team bus pulled away from the squad's hotel.
Bartra underwent surgery on a broken wrist after he was hit by flying glass, Dortmund president Reinhard Rauball said.
A policeman, who was on a motorcycle escorting the team bus, suffered trauma from the noise of the blasts, which shattered the bus windows.
Before the match began, fans chanted "Bartra! Bartra!", in support of the injured defender.
As the squad geared up for kick-off Wednesday, Dortmund's chief executive Hans-Joachim Watze vowed that his side would "play not only for ourselves today. We will play for everyone... we want to show that terror and hate can never determine our actions".
Interior Minister Thomas de Maiziere, who attended Dortmund's match, said the "fascination" surrounding football drove terrorists to try to disrupt it.
"That's why it's right that we do as much as we can to protect it, and not allow criminals to take the fascination away from us."