The explanation for why the founder and chairman of Barnes & Noble (BKS) sold nearly 2 million shares in the ailing bookseller this week is beginning to read like a B-list mystery novel.

Early Wednesday morning, the company reported that Leonard Riggio, Barnes & Noble's largest individual shareholder, liquidated $27.6 million worth of his personal stake in the company. The official filing with the Securities and Exchange Commission said that he did so for "tax planning purposes."

The news sent shares tumbling. After falling 12.5% the previous Friday due to an announcement that the SEC is investigating the company's accounting practices, they dropped an additional 4.3% in intraday trading on Wednesday, bottoming out at $13.40 midway through the morning.

As I noted at the time:

When the founder and largest shareholder of a struggling company sells $27.6 million worth of stock for "tax planning purposes," do you really think that's the reason behind the sale? Or do you suppose it could have something to do with wanting to abandon ship while there's still time?

That, however, wasn't the end of the story. By early afternoon, Riggio told Jeffrey Trachtenberg of The Wall Street Journal that the sale really was for the purposes of tax planning. The article fueled a recovery in the stock, which ended the day up by 2.3%.

According to Riggio, the transaction resulted in a loss of between $42 million and $52 million, allowing him to offset taxable gains from other investments. The article reported that he purchased the shares "in recent years for prices ranging between $35 and $40 per share, which translates to an approximate loss of between $21 and $26 per share."

To prove the point, the 72-year-old founder said that he doesn't have "any intentions of selling more shares."

But here's the thing. Less than a year ago, Riggio claimed to be "readying a bid" to take the ailing bookseller private. In a press release issued on Feb. 25, the company said that "Mr. Riggio plans to propose to purchase all of the assets of the retail business of Barnes & Noble."

The purported plan never came about and was officially put to rest in August when the bookseller admitted that Riggio had "suspended his efforts to make an offer for the company's retail business."

But the question now is: Why the change of heart? And more specifically, does his decision this week to double down on the reversal by selling 2 million shares have anything to do with it, or is it merely coincidental?

Is it because the company sunk tens of millions of dollars into an ill-fated attempt to compete with the likes of Amazon.com and Apple in the hardware space? Is it because Barnes & Noble's core business is sinking faster than a scuttled battleship from a Tom Clancy novel? Could it have something to do with the fact that the company is so disheveled right now that it doesn't even have a permanent CEO? Or what about that SEC investigation?

The point I'm trying to make is that his claimed need to merely offset gains just doesn't seem to add up. The shares he's selling aren't a recent addition to his stake in the company. According to the figures reported by the Journal, they most likely date back to 2007 or earlier. In other words, this is a chunk of his core holdings in the company.

Now, let me be clear: It's hard to blame Riggio if this is indeed the first salvo in an effort to monetize his ownership interest in Barnes & Noble. At the same time, however, current shareholders in the company should think twice before accepting the explanation that this was nothing more than a benign tax maneuver.