By Oliver Woods BBC World Service business reporter

Frank Quattrone could face 25 years in jail

The former investment banker Frank Quattrone stands charged with trying to obstruct official investigations into the Wall Street flotations of technology shares.

Soon after the authorities finished laying out their case against Mr Quattrone, the former Wall Street star became the trial's primary witness.

During the dot.com boom, Mr Quattrone made vast amounts of money both for himself and for his bank Credit Suisse First Boston (CSFB) by bringing companies including Amazon and Cisco Systems to the stock market.

Dramatic

The prosecutors have said Mr Quattrone sent an email to colleagues advising them to "clean up" old files relating to Initial Public Offerings, shortly after being told that CSFB was under criminal investigation.

He's as honest, ethical, straightforward as any human being I know. Character witness Rosario Lamberto

CSFB later paid $100m (�60m) to settle charges that it had wrongly given shares in so-called "hot" internet flotations to favoured clients in return for banking fees.

His testimony began dramatically.

Speaking directly to the jury, he calmly denied that he had obstructed an investigation by America's stock exchange regulator, the Securities and Exchange Commission (SEC).

He also denied intent to obstruct a grand jury investigation.

Honest

Ahead of Mr Quattrone's testimony, a character witness who had known him since they were six years old said: "Frank and I were raised in an ethnic middle-class neighborhood."

"He's as honest, ethical, straightforward as any human being I know," added Rosario Lamberto.

"I would literally place my life and the life of my wife and children in his hands." Quattrone faces a maximum prison term of 25 years and fines totaling $750,000 if convicted of all the charges against him.

Technology boom

Mr Quattrone was one of the first to spot the rise of the technology companies.

He is said to have earned himself at least $200m during the dot.com boom, while bringing in fees for CSFB of more than $1bn.

His trial will be being watched closely by former executives at Enron and Worldcom, who are also awaiting trial.