HALIFAX -- Lawyers arguing the case of a disgraced naval officer who sold military secrets to Russia gave conflicting accounts of the damage his treachery did to Canada's foreign relations, with one referring to it as "theoretical harm" while the other claimed it endangered the lives of Canadian intelligence agents.

Mike Taylor, the lawyer for Sub-Lt. Jeffrey Paul Delisle, pressed Crown witnesses repeatedly Thursday to reveal evidence of real damage done by the officer's relationship with Russian agents who paid him almost $72,000 over nearly five years for a treasure trove of classified data.

Taylor challenged Brig-Gen. Rob Williams, director general of military signals intelligence, on assertions that the damage Delisle did to relations with Canada's allies was irreparable and severe, as stated in a CSIS assessment.

Taylor asked if he had been told by any of the so-called Five Eyes community members that Canada was not receiving intelligence.

"We have not been told we have been cut off," he said in provincial court in Halifax on the first day of Delisle's two-day sentencing hearing.

"(But) I would not say (it's) business as usual."

Wesley Wark, an expert in security and intelligence and the defence's only witness, also said it would be difficult for the Canadian intelligence community to prove Delisle caused much real damage because police intercepted only two attempted transmissions during the years he was selling secrets.

He said he hadn't seen any evidence of a Russian reaction or response to the material they received over the years.

"It is, in a way, theoretical harm," testified Wark, a professor at the University of Toronto. "To be honest, it is very difficult to assess the harm he has done."

He dismissed the Crown's assertion that Canada is at risk of being cut off from intelligence-sharing with its partners, saying that more serious breaches in other countries have not resulted in them being frozen out.

"It is a real reach to say that Canada will suddenly be cast out," he said. "I can't imagine we'll be cast out."

Delisle, 41, sat alongside his lawyer wearing a blue hooded sweatshirt as Crown attorney Lyne Decarie laid out her case in a tale of espionage that has captivated legal and security experts since he was arrested a year ago. His mother sat in the courtroom's front row, behind her son and between two courtroom artists.

Decarie said Delisle received 23 payments totalling $71,817 from 2007 until 2011 after he walked into the Russian Embassy in Ottawa to offer his services for money.

She said Russian agents told him to provide a "manuscript" on the 10th of each month with information pertaining to Russia.

Decarie said Delisle came under suspicion after returning to the country in September 2011 from Brazil, where he met a Russian agent named Victor who told him that he would become a "pigeon" or liaison for all Russian agents in Canada.

Alarms were raised within the Canada Border Services Agency because he had no tan, little awareness of the tourist sites in Rio de Janeiro, three prepaid credit cards, thousands of dollars in U.S. currency and a handwritten note with an email address, she said.

She outlined how Delisle acquired and then transferred classified information to the Russians by searching references to Russia, copying them onto a floppy disc on his secure system at work, took it to an unsecure system and pasted it onto a memory stick.

He then took the information home and copied it into an email address that he shared with his Russian agent so he never had to send the email, Decarie said.

Michelle Tessier, director general of internal security at CSIS, told the court "a lot of resources" have been diverted to reassuring Canada's allies that their information is safe.

She testified that she has been dealing with the Five Eyes group, which includes Canada, Great Britain, the United States, New Zealand and Australia, who she said have decided to "increase the safeguarding of information" following Delisle's actions. She didn't elaborate.

Delisle's crimes could mean that CSIS receives less intelligence and, at the extreme, lives could be lost, she said.

"There's a risk we might be cut off of certain intelligence," Tessier told the court when asked by the Crown what might happen if the agency doesn't meet deadlines to repair the damage.

Two CSIS documents that Delisle tried to transmit to the Russians on Jan. 11, 2012, just before he was arrested, contained information that could potentially identify sources that work for CSIS, she said.

She said CSIS is continuing to assess the fallout from Delisle's actions.

"It is an ongoing process," she said.

"We take employee identity very seriously. ... It could be threatening to their own safety."

The damage that could have been done had those reports been transferred to the Russians would have been high because they contained "tactical pieces of intelligence," she said, adding that it could discourage potential sources from coming forward to CSIS.

"If the service (CSIS) is not able to show it can protect human sources, that will have a chilling effect on the recruitment of human sources," she said.

"Knowing this took place over a five-year period is extremely concerning, especially (because) there is a lot we still don't know.

"Mr. Delisle volunteered. He wasn't even recruited. For us, that has a significant impact."

The testimony from the Crown witnesses contrasts with the federal government's position. Defence Minister Peter MacKay has said that Delisle's breach had not damaged Canada's relationship with its allies.

"Our allies have full confidence in Canada," MacKay said after Delisle was charged.

Delisle pleaded guilty in October to one charge of breach of trust and two charges of passing information to a foreign entity that could harm Canada's interests. He is the first person to be sentenced under Canada's Security of Information Act, which was passed after the Sept. 11 attacks.

The breach of trust charge carries a maximum sentence of five years, while the other charges each carry a life sentence.

Delisle joined the navy as a reservist in 1996, became a member of the regular forces in 2001 and was promoted to an officer rank in 2008.

His sentencing hearing is scheduled to end Friday.