I heard Bitconnect's owners collected BTC50000 from people and scammed them. the owners sold BTC50000 from 2 days ago till now. This is a big reason for crashing price. don't panic and put some buy orders at different lower price. If BTC fall down to $1500 don't panic and do buying more at different steps.
if this true, this can be one from many reason
because there are a lot of reason for the down price of Bitcoin in this moment
but, i think bitcoin will never comeback to $1500 that is very imposible for me