Complex sentence: The following day a Swedish newspaper reported that similar attacks had taken place in Stockholm in 2014 and 2015, when female participants at "We Are Sthlm", a teenage music festival, had complained of being surrounded and molested by groups of men.
Split into simpler sentences: The following day a Swedish newspaper reported that similar attacks had taken place in Stockholm in 2014 and 2015. Female participants at "We Are Sthlm", a teenage music festival, had complained of being surrounded and molested by groups of men.