Dortmund said on Twitter on Saturday Bartra had been released from hospital. Had the bombs been detonated even one second earlier, many people would have been seriously injured and some may have been killed, Bild am Sonntag newspaper cited an investigator as saying. Welt am Sonntag said police thought further attacks were possible, citing a document sent to regional police headquarters as saying that soccer games, rock concerts and cultural events were particularly at risk. It said regional police wanted to have a greater presence if necessary and use dogs trained to sniff out explosives. INCREASED SECURITY Joachim Herrmann, interior minister of the state of Bavaria, told the same newspaper Bavaria planned to use more video surveillance, especially in crime hotspots and in public places - a controversial issue in Germany, where memories of the Nazi Gestapo and the Stasi security police still linger. Joachim Thomas, chairman of the association of German stadium operators, told Welt am Sonntag he believed full-body scanners would be used at entrances to stadiums in future. Police are overstretched already and do not have enough staff to keep watch over a team's hotel night after night so clubs would have to provide extra security staff if they wanted that, said Arnold Plickert, GdP police union's deputy chairman. Security was tight for Saturday's matches, including a Bundesliga game between Dortmund and Eintracht Frankfurt. Dortmund police posted a picture on Twitter showing an armed officer outside the stadium, saying they had provided more security inside and out.