A 28-year-old arrested on suspicion of bombing the bus carrying the Borussia Dortmund football team last week was motivated by financial greed, prosecutors said.
A Dortmund player and a policeman were injured in the triple blasts as the bus was heading to the team's stadium for a Champions League match against AS Monaco.
The German-Russian citizen was arrested on Friday in Germany.
Prosecutors said the suspect, identified only as Sergej W in keeping with German privacy law, was arrested by a police tactical response team in the early hours in or near the southwestern city of Tuebingen.
The man faces charges of attempted murder, causing an explosion and serious bodily harm.
Prosecutors said they planned to make a statement later, but revealed that the suspect had taken out a loan and bought a large number of so-called put options for shares of Borussia Dortmund, betting on a drop in the share price.
"A significant share price drop could have been expected if a player had been seriously injured or even killed as a result of the attack," they said.
Ralf Jaeger, the top security official in North Rhine-Westphalia state, said the suspect had hoped to earn millions.
"The man appears to have wanted to commit murder out of greed," said Mr Jaeger.
Prosecutors said they were able to trace the computer used to purchase the put options to the luxury hotel in Dortmund where the team had been staying.
They said the suspect had also booked a room there and placed three explosives, packed with shrapnel, along the route the bus would take to reach the stadium.
"The explosive devices were detonated at the optimum time," prosecutors said, noting that the team bus was equipped only with security glass and not reinforced glass.
Several windows on the bus were shattered in the blasts, injuring defender Marc Bartra. A police officer accompanying the bus also suffered trauma from the blast.
Investigators found notes at the scene claiming responsibility on behalf of Islamic extremists, but quickly doubted their authenticity.
The notes demanded that Germany withdraw reconnaissance jets assisting the fight against Islamic State group and close the US Ramstein Air Base in Germany.
But experts said the letter's mix of correct, complicated German and obvious mistakes suggested it was a red herring, as were two subsequent claims pointing to left-wing and right-wing extremists.
The club thanked authorities in a statement on Facebook: "The fact that no further people were injured or killed was, as we now know, purely a matter of luck."
Captain Marcel Schmelzer said the team hopes to learn further details about the background to the attack.
He added: "This information is important to everyone who sat in the bus because it would make it significantly easier to process (what happened)."