We don't yet definitively know why the deaths occurred. However, the City says both ravers were “involved” with MDMA, and it's reasonable to speculate that the two OD'd. Yesterday was also a swelteringly hot day to be on Randall's Island. Dehydration may have played a factor.
Armin Van Buuren, Sebastian Ingrosso, Steve Aoki, Zedd, and Diplo were scheduled to perform today. Diplo had previously made noise by promising to break the world record for “mass twerking.”
Here's the statement from the concert's founders:
The founders of Electric Zoo send our deepest condolences to the families of the two people who passed away this weekend. Because there is nothing more important to us than our patrons, we have decided in consultation with the New York City Parks Department that there will be no show today.