A 28-year-old man was arrested on Friday in connection with the Dortmund team bus bombing, with German police investigating an unusual possible motive of stock market speculation, according to German publication Bild.
Essentially, the police believe that the suspect, Sergej W, was trying to profit from the team's loss of assets—in this case, human life—by shorting his stocks of Dortmund, the only German team that is publicly traded, and then targeting the team's players. Bild reports that he bought 15,000 put warrants for $83,420 on the day of the attack. If Dortmund's stock had plummeted in the wake of the bombing, Sergej would have stood to gain as much as $4.2 million, according to police.
Employees of the German bank Comdirect alerted police to the unusual option purchases made by Sergej as a possible money-laundering scheme. But police started to put together a few pieces of circumstantial evidence—including the suspicion that the various letters claiming conflicting responsibility for the attacks were inauthentic—that pointed to Sergej's possible connections to the attack itself.
Sergej W had booked a room at the team's hotel far in advance of the Champions League match, at a time when it wasn't certain when Dortmund would play their home matches against Monaco. He booked the hotel for both possible dates. Once at the hotel, he also asked for a room with a window facing out to the road where the explosives were later detonated. According to Bild, Sergej had been awarded a prize in technical engineering, suggesting a background in electrical engineering that could have potentially been used to create a detonator.
According to Bild, Sergej alerted hotel employees when, amidst the panic after the explosion, he calmly walked into the hotel restaurant and ordered a steak.