The CPI's investigation also reveals that of the top 100 officials in the Bush White House, 14 had significant stakes in the embattled energy company, including Secretary of Defence Donald Rumsfeld, Senior Presidential Adviser Karl Rove, and US Trade Representative Robert Zoellick.
Selling up
Enron's current troubles stem largely from its admission that from 1997 to 2000, it systematically overstated its profits to the tune of $600m, while keeping investments in executives' own sideline companies off the books.
The federal investigation, reported in the New York Times suggests that the share sales began in 1999, two years after the company's admitted misreporting of its profits began.
A total of $1.1bn was realised from then until mid-2001, the report says.
A lawyer for Enron, Robert Bennett, confirmed that an investigation was under way.
But, he told the newspaper, he remained "unaware of any evidence that supports the allegation there was improper selling by members of the board or senior management".
The newspaper said the company's chief executive, Kenneth Lay, was one of those who gained the most from the selloff - which the CPI says accounted for nearly half the total holdings of the 29.
Mr Lay made $101.3m, the paper says, one of more than a dozen top managers who made more than $30m.
Smoking e-mail?
The investigation is linked to the multiple federal and Congressional probes into why Enron executives were allowed to sell up while their employees - most of whose retirement plans were held largely in the company's shares - were banned from doing so.
As part of that investigation, Democrat Congressman Henry Waxman is demanding information from Mr Lay about e-mails he allegedly sent to his staff in August 2001 praising the company's financial position.
"If it is true that you sent those e-mails, then it appears that you misled your employees into believing that Enron was prospering and that its stock price would rise," Mr Waxman said.
On 14 August, according to Mr Waxman, Mr Lay e-mailed employees to say growth "has never been more certain".
And Mr Waxman said he had seen an e-mail from Mr Lay sent on 27 August to employees who had received stock options, saying that the highest priority was to "restore investor confidence in Enron... This should result in a significantly higher stock price."
But by then, according to Mr Waxman, the share price was nearly 60% off its peak of around $90 and Mr Lay had already offloaded $40m in Enron shares in 2001 alone.
Enron shares are now worth less than a dollar, having bottomed out at 26 cents on 30 November last year.
White House hooks
The CPI's investigations, meanwhile, point out that aside from the close personal friendship between Mr Lay and President George W Bush, over $600,000 has been given by Enron executives to Bush campaigns over the years.
An exact figure is difficult to draw from staffers' disclosures, since stockholdings are disclosed in wide bands.
Mr Rove was one of the biggest shareholders, with between $100,001 and $250,000 when he was appointed.
Mr Zoellick, meanwhile, held between $15,001 and $50,000 of stock.
And according to the Center for Responsive Politics, another Washington pressure group, nearly half the current US House of Representatives and three quarters of the Senate have taken the Enron dollar at some time, with a total of $5.8m in political donations being paid from 1989 on.
Most were donated in 1999-2000, in the runup to the most recent presidential election and during the time when Enron's finances were spiralling out of control.