Counterspin has a pretty good guess about who the mystery Harken stock buyer is.
One intriguing possibility is Lee M. Bass. He was a Bush Pioneer during his Presidential run, and a big supporter of his during his Gubernatorial campaigns. More importantly, as Texans for Public Justice reported:
"When Bush’s ailing Harken Oil suspiciously won exclusive offshore drilling rights in Bahrain in ’90, the Basses bankrolled the venture."
In fact, according to a May, 1999 New York Times Article, Bush's Lawyer, Robert Jordan, the current Ambassador to Saudi Arabia, argued that Bush thought he was selling his shares on the impending "good news" of the Bass investment in the Bahrain drilling venture.
UPDATE. Digby adds more analysis:
If it's Bass, then the ground shifts from insider trading to actual pay-off and Poppy becomes much more implicated.
Tiny nowhere company, Harken, gets huge Bahrain contract because Junior is on board and it will curry favor with 41. Bass, big time contributor to 41, gets most of the actual work from that Bahrain contract. Bass fortuitously buys Junior's stock just before it's set to tank (after having been pumped by the phony Aloha deal) thus allowing him to cash out and pay off his Texas Rangers loans, a deal which also allowed him to invest almost nothing and emerge a multimillionaire.
Now what could be suspicious about that?