According to a recent study by researchers from the University of Tulsa and Tel Aviv University, the massive increase in the bitcoin price in late 2013 was caused by suspicious trading activity on the now-defunct Mt. Gox Bitcoin exchange. The study, which is titled Price Manipulation in the Bitcoin Ecosystem, indicates that 600,000 bitcoins were acquired by agents who did not pay for them, and the bitcoin price rose by an average of $20 on days when the suspicious trading activity took place.

Source and More information: Study Late 2013 Bitcoin Bubble Fueled by Suspicious Trading Activity on Mt. Gox