The Congress enquiry is homing in on Enron
Having tackled the energy giant's executives and accountants, the investigators want to find out how much Wall Street bankers and stock market analysts knew about the real state of Enron's finances.
Enron became the US's biggest bankruptcy when it collapsed in December after distorting its accounts.
Congresswoman Diana DeGette from Colorado, a member of the Commerce and Energy Committee, said there were many questions she wants answered.
Conflicts of interest
"There are two main questions," she told the BBC's World Business Report.
"How did the Wall Street firms structure and sell Enron's limited partnership, and how is it that at the same time firms were issuing recommendations to buy Enron stock," she asked.
She claims that Wall Street also had inside knowledge about Enron's financial condition and questions the conflict of interest in investment firms.
The conflicts of interest issue has already permeated the scandal of the collapsed energy giant since Andersen was both its auditor and its consulting firm.
Ms DeGette said there was "an obvious fundamental conflict of interest".
Collusion
She believes many Wall Street investment banking firms need to tackle similar issues.
"This is quite a serious problem and what we're fearful of is that it will expand from Enron to other large corporations," she said.
She explained that there was a problem when you had collusion from both auditors and the investment advisors who are telling people that the stock is a good buy.
A Chinese wall structure is designed to keep knowledge separate from each department.
"But if you have one entity of a Wall Street investment firm which knows that the stock is inflated and there is a Chinese wall, and then you have investment advisors saying buy the stock - that is a problem," she said.
"That's why we really feel like we need to bring folks in front of our committee and find out exactly what was going on."
False impression
The committee suspects that those who were promoting the stock knew there was a problem, and yet they continued to do so regardless.
There is also the possibility that Enron has leant on analysts to persuade them to keep on seeing the company in a rosy light.
Ms DeGette said it was part of the grey area in investment banking and investor advising, because it's quite common to have seminars for stock analysts or to provide them with the company's perspective.