German investigators were hunting on Wednesday for possible suspects responsible for three explosions that rocked the Borussia Dortmund football team’s bus, injuring a player and a policeman. The assault, described by Dortmund city’s police chief as a “targeted attack” against the team, shook German football ahead of crucial Champions League ties, AFP reported. Investigations will focus on a letter claiming the attack, which was found close to the site of the blasts. German authorities have held off from describing it as a terror attack, saying it is too early to determine a motive. The explosives detonated minutes after the Dortmund team bus pulled away from the squad’s hotel and headed for their quarterfinal, first-leg, tie against Monaco. Spanish international Marc Bartra underwent surgery on a broken wrist after he was hit by flying glass. The injured policeman, who was on a motorcycle and had been escorting the team bus, suffered trauma from the noise of the blasts.