A hedge-fund founder once recognised as one of the richest citizens in the US would serve the longest sentence in history for an insider trading conviction if a federal judge grants the government's request to send him to prison for two decades.

Raj Rajaratnam's sentencing was scheduled on Thursday in Manhattan. Prosecutors are asking US District Judge Richard J Holwell to send the 54-year-old, one-time billionaire to prison for at least 19 1/2 years for his May conviction on securities fraud charges.

They say federal sentencing guidelines call for a sentence up to 24 1/2 years. The prosecution has placed Rajaratnam's profits from illegal trades between USD 70 million and USD 75 million, saying he moved so much money around within his multibillion dollar funds that the movement of price in individual stocks could be traced to his trading whims.

Lawyers for the Sri Lanka native argue that his sentence should be much lower 6 1/2 to 9 years for what they say was illegal profits of about USD 7 million, when the trades at his Galleon Group of hedge funds are disregarded.

The defense also has asked for leniency partly based on Rajaratnam's 'failing health' and his 'unique constellation of ailments'.

They say a lengthy prison term will amount to a death sentence. The sentencing culminates a series of convictions and sentencings that followed the October 2008 announcement of the arrest of Rajaratnam in what prosecutors labelled the biggest hedge fund insider trading case in US history.

In all, more than two dozen people were arrested. All were convicted with the sentences ranging from a few months to 10 years. Since the first arrests, US Attorney Preet Bharara has widened the probe.

A year ago, he said insider trading is 'rampant and may even be on the rise.' Using information gleaned from the many cooperators in the Rajaratnam case, prosecutors have focused lately on consultants who are paid to arrange conversations between employees of public companies and hedge fund managers.

Too often, prosecutors say, they have found a nest for insider trading rather than for the discussion of legitimate research.

In their pre-sentence submissions, prosecutors say Rajaratnam lacks remorse, even after a trial that featured the playing of dozens of taped conversations in which Rajaratnam was heard discussing financial news events that were not yet publicly known.

"Rajaratnam has neither acknowledged responsibility for his crimes nor remained silent. Instead, Rajaratnam's post-conviction statements show that he remains defiant that he never committed insider trading and, incredibly, he maintains that the line between legal and illegal conduct was not always clear to him," prosecutors wrote.

They quoted from a report that is not public that he told the Probation Department: "In my own mind, the line between permissible 'detective work' and impermissible insider trading was not always clear, especially with regard to companies broadly covered by the news media as to which there was a wealth of publicly available information, including frequent leaks, rumors and speculation about corporate transactions and other important developments."

The prosecutors wrote that Rajaratnam's comments 'do not reflect the proper respect for the jury's verdict, the evidence in the trial record or the laws against insider trading.'