The suspect, identified only as Sergej W. in line with German privacy laws, was arrested by a police tactical team early Friday near the southwestern city of Tuebingen, federal prosecutors said.
"We are working on the assumption that the suspect is responsible for the attack against the team bus of Borussia Dortmund," prosecutors' spokeswoman Frauke Koehler told a news conference Friday.
She said the man came to the attention of investigators because he had made "suspicious options purchases" for shares in Borussia Dortmund, the only top-league German club listed on the stock exchange, on the same day as the April 11 attack.
W. had taken out a loan of "several tens of thousands of euros" days before the attack and bought a large number of so-called put options, betting on a drop in Dortmund's share price, she said.
"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," according to prosecutors, though Koehler said the precise profit W. might have expected was still being calculated.
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," Jaeger said.
Investigators found notes at the scene claiming responsibility on behalf of Islamic extremists, which Germany's top security official, Interior Minister Thomas de Maiziere, said was a "particularly perfidious way to toy with people's fears."
He said the suspect had been under close surveillance for about a week and that the evidence against him was significant.
"The fact that someone wanted to enrich himself by killing people to influence the stock market is particularly reprehensible," he said.
The suspect faces charges of attempted murder, causing an explosion and serious bodily harm. He was brought before a judge, who ordered him held in custody after evaluating the evidence against him.
She said investigators believe W. acted alone - there are "no indications of possible helpers" - but would continue to probe the possibility he had accomplices.
Dortmund defender Marc Bartra and a police officer were injured in the triple blasts as the bus was heading to the team's stadium for a Champions League game. Bartra had to have surgery on his wrist and arm and is out of action for several weeks.
The team's shares did slide slightly after the attack, but quickly recovered.
Dortmund's first-leg match against Monaco was postponed and the team lost 3-2 to Monaco the next day. Dortmund coach Thomas Tuchel criticized UEFA and top soccer officials for forcing the team to play such a top-level match so quickly after an attack on their team.
Prosecutors said they traced the computer used to purchase the put options to the luxury hotel in Dortmund where the team had been staying. They said W. had also booked a room there and placed three explosives, packed with shrapnel, along the route the bus would take to reach the stadium for their match against Monaco.
"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. The bomb shattered several windows on the bus, wounding Bartra. A police officer accompanying the bus also suffered trauma.
The club thanked authorities in a statement. "The fact that no further people were injured or killed was, as we now know, purely a matter of luck," it said on Facebook.
Dortmund captain Marcel Schmelzer said the team needed to learn all it could about the attack.
"This information is important to everyone who sat in the bus because it would make it significantly easier to process (what happened)," he was quoted as saying.
After the three identical notes claiming responsibility for the attack were found at the scene, investigators initially considered the possibility that it might have been the work of Islamic extremists.
The notes demanded that Germany withdraw reconnaissance jets assisting the fight against Islamic State group and close the U.S. 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.
David Rising contributed to this report.
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