In a surprising twist, German prosecutors say the Borussia Dortmund bus bomber wasn’t an Islamic terrorist — he was a trader trying to make a quick euro betting shares of the soccer team would fall.

A 28-year-old suspect, identified as Sergej W., bought 15,000 put options in Frankfurt-listed Borussia Dortmund BVB, -1.54% on April 11, the day of the blast, investigators said in a statement Friday. Eight days earlier, he took out a consumer loan, they noted.

The Russian-German suspect, arrested Friday in Tuebingen, central Baden-Württemberg, hoped to trigger a slide in shares to line his pockets, federal prosecutors contend.

“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.

Put options give the owner the right to sell a set number of shares at a specific price by a predetermined date — in this case, June 17. The Borussia Dortmund team was due to play against Monaco to try to retain a berth in the Champions League.

German public TV broadcaster ARD reported that put options bought just ahead of the attack were so “out of money” — a strike price that is lower than the market price of the underlying asset — that buyers must “either have been extremely inexperienced or expecting a sharp fall in prices.”

North Rhine-Westphalia Interior Minister Ralf Jaeger, the top security official in the state, said the suspect invested €79,000 ($85,000) in the stock options, which would have meant a profit of more than 1 million euros if the share prices had sunk, according to The Wall Street Journal.

Shares of Borussia Dortmund fell 2% on the day of the attack, rose 1.75% on April 12, then dropped another 3.8% on April 13. Last week marked the worst week for those shares since Dec. 16, with a drop of 3.16% and the third straight weekly loss.

The month of March for Borussia Dortmund, with a gain of 10%, was the best for shares of the football team since an 18.5% surge in October. Year-to-date, shares are up 6.7%. For the current week, shares are down 2.1%.

Shares of Borussia Dortmund over the past seven days MarketWatch

The team was eventually beaten 3-1 by Monaco in the game that was rescheduled after the blast.

The attack left one player seriously injured when the windows of the bus shattered. But officials have said the situation could have been much worse if the explosives had been placed elsewhere.

Three shrapnel-packed bombs were placed along the road the bus was taking to get to the stadium. Prosecutors said the suspect also booked into the Dortmund hotel where the team was staying.