Notes in Russian and Cyrillic sketching out attack plans were found hidden in the suspect's apartment in Rottenburg in Baden-Württemberg (BW) state, reported "Die Welt" and "Süddeutsche Zeitung" on Friday.

The notes included details on the detonators and remote control frequencies used in the April 11 attack on the bus as the Borussia Dortmund (BVB) team drove past an explosives-laden hedge while departing its training hotel for its Dortmund stadium.

The three shrapnel-loaded devices exploded, injuring one team player and a police officer.

"The documents were well hidden. So well, that the investigators of the Federal Criminal Office (BKA) did not initially find them," reported "Die Welt."

It added that investigative sources still believed that Sergei W., a Russian-German national, acted alone.  Federal prosecutors have not commented on the latest claim.

The 28-year-old Sergei W., whose full name remains obscured under Germany's privacy laws, has - via his defense lawyer Reinhard Treimer - denied staging the attack from a hotel room. But prosecutors allege Sergei W. wanted to make gains on BVB share options by killing as many players as possible.

Bartra returns to training

On Wednesday, injured BVB player Marc Bartra from Spain, whose wrist was fractured by the blasts, returned to training, saying he wanted to be with his teammates " like never before."

"The pain, the panic, the uncertainty, it was the worst in my whole life," said Bartra, still wearing a protective cast on his arm.

"The doctor told me that the bone was broken by the explosion and the splinters, but the tendons and ligaments were fortunately not affected."

ipj/rc (SID, AFP)