I am nervous when a director sells so I did a bit more digging. Peter Richards is also the chairman of Graincorp (GNC), Elmore Ltd (ELE - suspended) and Emeco Holdings (EHL). Of interest, he owns more shares and options in CRO than any of these other companies, despite offloading 3m CRO shares.
When considering GNC, EHL and ELE his modus operandi is not to be invested in the companies he is governing. Perhaps he is awaiting free of cheap shares from these companies to offload.
