Were the books cooked? Was wrongdoing uncovered? Is management fighting? Are more changes coming?

Alarm bells almost always sound when a key executive leaves a bank unexpectedly. And in the absence of a good explanation, they are likely to keep on ringing.

But coming up with a solid explanation almost always is tricky. If the departure is the executive's own choice, even for reasons beyond reproach such as a personal illness or a family matter, a bank must weigh the thirst for a back story against any privacy wishes the executive might have. And if the departure comes at the behest of someone else within the bank, the company walks a fine line between supplying details and airing its dirty laundry.

"Every situation is different, and there's no book on what to do," said Fraser Seitel, a public relations consultant who was the longtime public affairs chief for the former Chase Manhattan Bank. But his rule of thumb is that "the company comes first," even at the expense of a departing employee's privacy, "because suspicion and rumors are going to dominate, and if you don't fill the vacuum, somebody else will."

It sounds like a strategy tailor-made for an age in which anyone with a Twitter account can sling commentary around the globe, and for a climate in which banks are under pronounced levels of scrutiny. But Seitel said the lesson could be drawn from an episode more than three decades old, when a banker named Al Rice was unceremoniously let go from the old Bank of America. Offering no details about why the company's heir apparent was leaving, the bank fueled rampant speculation that culminated with a grand jury investigation. As detailed in Moira Johnston's "The Tumultuous History of the Bank of America," Rice had been accused by his boss of self-dealing. But the bank was unwilling to publicize that at the time of his departure.

More than 30 years later, banks are continuing to court suspicion with vague press releases about executive resignations. Regions Financial Corp. raised red flags in November with the announcement that three executives — the chief risk officer, the director of credit risk and the head of problem-asset management — had left the Birmingham, Ala., company. Regions shares fell more than 4.5% in the first trading session following the announcement.

On Wednesday, Wells Fargo & Co. shares dropped 2.8%, far outpacing the KBW Bank Index's 1% decline for the day, as word spread about the late-Tuesday resignation of Chief Financial Officer Howard Atkins. Aside from noting that Atkins "turns 60 this week," the press release was vague on details. Wells Fargo ascribed the departure to "personal reasons" and declared that the retirement "is unrelated to the company's financial condition or financial reporting."

But the usual arrangements surrounding the departure spurred questions about the matter. Atkins was replaced immediately, but he will go on an "unpaid leave of absence" until August, when his retirement is effective officially. Reflecting the unorthodox manner of Atkins' leaving, the financial news website TheStreet.com topped its reporting on the story with a headline that read: "Wells Fargo CFO 'Retires' Unexpectedly."

But William Fitzpatrick, an analyst with Optique Capital Management, wasn't concerning himself with reading too far into the announcement, saying he "would tend to take it on face value that [Atkins] is just moving on."

And if the reason turned out to be illness, like the one that led Steve Jobs to step down as the chief executive of Apple?

"The CFOs aren't the visionaries for the companies. They are the number crunchers," Fitzpatrick said. "And with the bigger companies, for me as an analyst, there's a comfort level that they have a deep bench" of number crunchers.

And if the dismissal were akin to the expense report scandal that got Mark Hurd fired as the CEO of Hewlett-Packard Co. (and led to a more salacious trail involving a former reality television contestant)?

"I'd look right over it," Fitzpatrick said. "It would be a sad story, but it wouldn't affect the equity valuation" of the company — at least not much beyond Wednesday's decline, he said.

Sometimes companies are even terser in their announcements about executive departures. To wit: the two-sentence regulatory document filed Wednesday by Freddie Mac. In the first sentence, the mortgage finance company announced that Bruce Witherell has resigned as chief operating officer, effective immediately, for personal reasons. The second sentence simply advised that Witherell would not receive any termination benefits.

By that standard, Wells was loquacious, even effusive, in announcing Atkins' resignation. But not everyone gave the company the benefit of the doubt.

Karl Denninger, who blogs about the markets on his own website, market-ticker.org, and has nearly 12,000 followers on SeekingAlpha.com, had a post on both sites Wednesday addressing Atkins' departure.

"When a top executive leaves on no notice and without a detailed and accurate explanation? It stinks like dead fish," he concluded.

Denninger, a former Internet entrepreneur who now trades for himself, said in a phone interview that he has no position in Wells Fargo shares — just a suspicion that there is more to the story than the company has let on.

A board issues an announcement light on details "with full knowledge that it's going to get raked over the coals by people like me, which means that whatever the situation is, it's worse than keeping your mouth shut," Denninger said. "I can't put my finger on anything. I don't even have any good rumors. All I know is there is no disclosure. So I have to assume it's not as simple as it's being explained, and the market seems to agree with me."