Prosecutors also said the three explosive devices contained metal pieces.
Two letters claiming the attack on Tuesday evening were being investigated, they said.
Prosecutors are treating the blasts as a terrorist attack but say the precise motive is unclear at present.
Chancellor Angela Merkel on Wednesday said the attack was “an appalling crime” and praised the fans of both Dortmund and their Champions League opponents, Monaco, for coming together.
Fans later filled Signal Iduna Park in Dortmund for the rescheduled quarter-final first-leg, which kicked off at 18:45 local time (16:45 GMT). Dortmund lost 3-2.
Afterwards, Borussia Dortmund manager Thomas Tuchel said his club felt “completely ignored” over the rescheduling of the match.
“We would have liked more time to take stock,” he said.
Inside a hotel close to the Dortmund stadium, several of the Monaco team told me how they discussed going ahead with the match.
Some were worried about the implications of the attack, and the risk of more danger, but felt reassured by German security, and ultimately felt to postpone was to give in, and that they were not prepared to do. The players’ bus waiting outside was under constant surveillance by armed police.
As the match finally got under way this evening, under intense security, all fans sang “You’ll Never Walk Alone” together. Players warming up applauded the support.
One fan said his wife would not let him bring his children because “the mass congregation of people outside made the venue too big a target”.
Others were defiant. German and French fans said they had become used to living with the threat of terrorism, and would not be stopped from enjoying their lives: the game would go on.
Dortmund fans open homes to stranded away supporters
Dortmund player Nuri Sahin gave an emotional interview after the match, saying: “Last night I didn’t realise what happened and, when I was at home, my wife and my son were waiting for me in front of the door and then I felt how lucky we were.
“We love football, we suffer with football. I know we earn a lot of money and have a privileged life, but we are human beings. There is so much more than football in this world and last night we felt it.”