Talk about key man risk. SAC Capital, does not just bear the initials of founder Steven Cohen. He dominates the Greenwich trading floor that has churned out such enviable investment returns and built his reputation as a star trader. And over half the $14bn under management is said to be his own fortune.

Why would somebody buy a significant stake in a firm that appears to depend so heavily on an individual and remains privately-owned - at least for now? There is added uncertainty because Mr Cohen is attempting a shift of emphasis away from his trademark quick-fire trading towards a less proven model of longer-term activist investing.