edit: The futures markets may not have even been the catalyst for this drop, more likely it's this: "The market has also been artificially pumped up by Bitfinex and their money printing machine Tether."
The timing of increased volumes and the beginning of bulk selloffs times pretty closely with the announcement of a large hack in South Korea — and exchange called Youbit. They've completely shut down. South Korea is a huge market.
https://themerkle.com/youbit-hacked-again-closes-its-doors/
https://coinmarketcap.com/currencies/bitcoin/historical-data...
> The South Korean National Intelligence service believes that North Korean hackers were behind that attack, as well as a separate hacking of South Korea’s largest exchange, Bithumb, back in February. The Korean Internet and Security Agency is currently investigating Youbit’s most recent attack.