Insider sales are apparently the new "hot button" on this board, however, trying to predict future price movement based on insider transaction data is, for the most part, pointless. A number of studies, including "The Relation between Aggregate Insider Transactions and Stock Market Returns", has found that "investors cannot use aggregate insider transactions to profitably predict future market returns."
So, what are insider transactions highly correlated with? Not surprisingly, it's the overall return on the market. That's right, the selling is driven by macro events more than anything else. Beyond that, many of these transactions are being motivated by diversification or liquidity needs. So, there is no great conspiracy theory. I'm not saying it never happens but the data simply doesn't support the theory.
