A few factors i believe have caused this sudden downturn..

a) Weak volume,if you watch the last few weeks ...the volume went BTC dropped increased significantly...in comparison to a weaker buying trend when it shifted from 9-10k,even weaker when it hit 11k.
Weak buying volume kills any financial market and makes it ripe for manipulation..

1. Consumer sentiment or lack there of...in other words disinterest. I think BTC dropping to 5800 scared alot of the newbie investors that jumped on the "Lambo/unicorn" train. They never saw it coming...panicked and ran out.
2. I agree with the assumption that selling those BTC weakened market conditions but didn't crash it....now it might have triggered bots to sell according to their algorithm (might explain the suddenly spike in trading volume when it would selloff)

Mt Gox is part of the problem...but not THE problem.