Fastow sent down for six years over Enron collapse

But the judge in Houston, Texas, Ken Hoyt, did not hand down the maximum 10-year term on the grounds that Fastow had shown remorse and co-operated with government officials.

In 2004, Fastow had agreed to serve as long as 10 years in exchange for testifying against the former top executives of the energy company, which has now become synonymous with corporate accounting scandals and fraud.

Evidence provided by Fastow helped secure the convictions for conspiracy and fraud of Enron's founder, Kenneth Lay, and the former chief executive Jeffrey Skilling. Hoyt described Fastow as having been “drunk on the wine of greed” but acknowledged that the former chief financial officer had demonstrated remorse by fully co-operating with government and civil lawyers in lawsuits against Enron.

“These factors call for mercy,” the judge said. Fastow has accused 10 leading investment banks of helping Enron falsify its accounts in return for lucrative advisory fees.

The accusations are made in a 24-page legal declaration filed by Fastow in support of a class action lawsuit against the banks brought on behalf of Enron’s shareholders.

In his statement, Fastow said he viewed the banks as well-paid “problem-solvers” who knowingly helped Enron create fictitious financial structures that made Enron appear far more profitable than it really was.

Attorneys for Enron shareholders, led by Lerach Coughlin, have already won $8 billion in settlements from a group of banks that includes Citigroup, Bank of America and JP Morgan.

Fastow was originally charged with 78 counts of fraud, conspiracy and money laundering, with 31 counts added later. As the sentence was announced in court, Fastow hugged his wife and was immediately taken away by officers. He will be sent to a low-security prison in Bastrop, Texas. When he is released he will be under a two-year supervision order.