This isn't hard. There was people there injecting people with needles containing an unknown drug.
This caused the crowd to panic and Rush the stage which in turn caused people to be crushed to death
So the people with the needles are directly responsible for the crushing deaths
The event staff is negligent for allowing the place to become too overcrowded
Also there were police officers there taking pictures while casualties were happening right behind them so they are negligent also
Yes it is easy, if we know who the people are jabbing others with needles we'll be able to untangle this web. However, I am surprised, stunned really that people were allowed into that packed, crowded venue with needles. Don't they have to walk through metal detectors? I saw video of people entering that place and packed in afterwards and it would not take much to convince me that the event organizers were negligent. The law is simple, if you are responsible for a safety hazard that results in people being killed then you are guilty of negligent homicide.
From what I gather the people were not killed directly by the needles. Still if you commit a crime in which people are killed as a result then you also are guilty of 2nd degree murder.
So for the moment forget about the civil suits, the issue right now is criminal. You will have a much stronger case in civil court if they are already convicted of negligent homicide and 2nd degree murder.