(BERLIN) — Six men detained over concerns about a possible attack on Berlin’s half-marathon were released Monday after investigators found no concrete evidence to back their initial suspicions, German officials said. Berlin prosecutors said the six men, aged 18-21, were released after their investigation, including the evaluation of data stored on electronic devices, turned up insufficient evidence to keep them in custody. The six were detained Sunday, the day of the race, and daily Die Welt reported police foiled a plot to attack race spectators and participants with knives. Police said later Sunday they had received vague indications of a possible attack plot and had taken action because of a generally high threat level, but had no “concrete indications” an attack was planned. The investigation is still ongoing.