A police study released on Tuesday (12/19) has determined the factors behind the incident at Denmark's Roskilde festival last June, in which nine concert-goers were killed.

According to the Associated Press, the study said that poor sound quality prompted fans to surge toward the stage during Pearl Jam's set, and that confusion regarding who should stop the concert compounded the tragedy. Investigators decided that no further criminal investigation was necessary.

The 24-page investigator’s report was based on 977 interviews with band members, organizers, rescue workers and others, according to AP.

Earlier this week, Oasis and Pet Shop Boys--both of who cancelled their Roskilde performances following the incident--announced that they had reached an agreement with tour organizers in which both bands’ performance fees will be used to improve safety measures at future festivals, and will also be donated charity.

Next year’s Roskilde festival will take place from June 28-July 1, according to the festival’s official website.