The explosives used in the attack on the Borussia Dortmund team bus may have come from the German military, local media report, citing sources close to the investigation.
Around 100 investigators from the German Federal Criminal Police Office (BKA) are looking into the incident, one of whom spoke to the Welt am Sonntag newspaper on Saturday.
“The explosives in the pipe bombs, which were filled with metal pins, might have come from the stocks of the Bundeswehr [German armed forces], but that’s still being checked,” the newspaper quoted the anonymous investigator as saying.
The source added that specialized training was needed to use the military detonators, which are hard to acquire.
A spokeswoman for the federal public prosecutor’s office declined to comment on the newspaper’s claims.
Three explosive devices went off near Dortmund’s team bus as it was transporting players to their match with Monaco on Tuesday evening, causing defender Marc Bartra to require surgery to his arm and wrist.
Although an Iraqi man, who is a suspected member of Islamic State (IS, formerly ISIS/ISIL), was arrested in connection with the blast on Thursday, authorities say there is no evidence to suggest that he was directly involved. A letter claiming responsibility was found at the scene of the crime ostensibly linking it to IS, but for the militant group to claim responsibility in this way is highly unusual. The letter also gave no religious justification for the attack, and an investigator told Bild newspaper that far-right extremists may actually be responsible.
According to Welt, police believe more attacks targeting high-profile venues and events, such as football matches or pop concerts, could be possible, so surveillance and security at these vulnerable spots should be stepped-up. A corresponding letter has been sent to regional police headquarters.
“In Bavaria, we are planning more intensive video surveillance especially of crime hotspots and public places,” Bavarian Interior Minister Joachim Herrmann told the Welt.
“Additionally, the video surveillance strengthens the population’s sense of security and can act as a deterrent to potential perpetrators,” he said.
Germany’s security services have been on high alert since December of 2016, when a truck driver drove into a Christmas market in central Berlin, killing 12 people and injuring 56. Germany also saw a wave of smaller terror attacks last summer. In July, a rejected asylum seeker blew himself up outside a wine bar near a music festival in the German town of Ansbach. That explosion injured 15 people.
The same month, a 17-year-old Afghan refugee attacked passengers on a train in Wuerzburg, wounding five people. The attacker was shot dead by police, who later found a handprinted Islamic State flag in his room.