An alleged insider trading duo were barely adults but working for investment banks "that paid them lots of money" when they allegedly struck an illegal deal to cash in on confidential information, a court has heard.

The criminal trial of Oliver Curtis, husband of Sydney public relations queen Roxy Jacenko, entered its final stages on Thursday as the Crown delivered is closing address to the jury of 12 men and women in the historic St James Supreme Court in Sydney.

Mr Curtis, 30, exercised his legal right not to give evidence in the trial. He has pleaded not guilty to a charge of conspiring with his then best friend, John Hartman, to use confidential information to rake in profits betting on the sharemarket.

Crown prosecutor David Staehli, SC, said in his closing remarks to the jury there was no dispute the duo engaged in 45 trades that netted them $1.43 million between mid-2007 and 2008.

The profits, in some cases totalling hundreds of thousands of dollars in one hit, were "not to be sneezed at for two young men", Mr Staehli said.

The St Ignatius' College, Riverview, old boys were then aged about 21 or 22 and were only "just adults, really, in one sense", Mr Staehli said, although they were working in boutique investment banks in the Sydney CBD "that paid them lots of money".

"This was a rort in which, in my words, both were involved," he said.

Mr Hartman, the prosecution's star witness, has already served 15 months behind bars for a string of insider trading offences, most of which related to his own trading.

He has given evidence he struck an illegal deal with Mr Curtis to pass on tips based on confidential information he gleaned from his job as an equities dealer at boutique investment firm Orion Asset Management. Mr Curtis denies the agreement was made.

The "confidential, price-sensitive" information was used to buy and sell so-called contracts for difference to bet on shifts in share prices and the pair split the profits 50-50, Mr Staehli alleged.

"Mr Hartman might not be a rocket scientist but plainly he's no fool," he said.

He said Mr Hartman realised that when he traded in shares for Orion he could influence share prices "and at the end of the day that's an incredibly important fact in this case".

"And what did he do? He started to take advantage of it himself by insider trading," he said.

But Mr Hartman's broker "apparently smelt a rat" in January 2009 and had in fact reported suspicions about his trading in 2008 because he "often seemed to be successful" in risky trades.

"Eventually, as it happened, Mr Hartman found himself at risk of being reported and ultimately he sought to pre-empt action that may have been taken against him by authorities by going to see [the Australian Securities and Investments Commission] with his lawyer," Mr Staehli said.

Mr Staehli said Mr Hartman told ASIC of Mr Curtis' alleged involvement at his first interview on January 21, 2009.

Later, his insider trading sentence was discounted because he agreed to give evidence against Mr Curtis in this case.

But Mr Staehli said there was not a "shred of evidence" that Mr Hartman's "revelations" about Mr Curtis were conditional upon a deal that he would be treated more leniently.

Counsel for Mr Curtis, Murugan Thangaraj, SC, is expected to start delivering his closing submissions to the jury on Friday.

Justice Lucy McCallum will then deliver her summing up before the jury retires to consider its verdict.