New York, April 19 (IANS) As hedge fund tycoon Raj Rajaratnam's lawyers rested their case with a finance professor's testimony that he did not trade on inside information, prosecutors played a new wiretapped phone call to rebut the defence.

Sri-Lankan born Galleon Group co-founder Rajaratnam's attorneys rested their case Monday without calling him to testify in his own defence as testimony concluded in the biggest insider trading trial in the US.

The defence called just five witnesses over six days, in contrast to the prosecution, which called 18 witnesses over five weeks. Closing arguments are set to begin Wednesday.

Prosecutors wrapped up their case Monday with FBI Special Agent James Barnacle introducing last of some wiretapped phone calls to counter the defence contention that 53-year-old Rajaratnam traded only on information that was already in the market.

In the conversation, recorded Sep 30, 2008, Rajaratnam and hedge fund consultant Danielle Chiesi are heard discussing a tip that Advanced Micro Devices was planning to spin off much of its semiconductor manufacturing operations to an Abu Dhabi investment fund.

The two had been quietly buying up the stock, but that day someone placed an order to buy one million shares just as the market was closing. The two try to figure out who is behind the order.

"Do you think somebody knows what we know?" Chiesi asks. "I think it's hard to believe."

Rajaratnam agrees the order probably just came from a market maker in the stock, not someone with inside knowledge of the upcoming deal.

"It's been widely speculated," Rajaratnam says about the AMD transaction. "What people don't know is the time."

Rajaratnam faces 14 counts, including conspiracy and securities fraud, in an alleged inside trading scheme that prosecutors say netted him as much as $63 million. If convicted, he could face 20 years in prison.