HALIFAX -- Christopher Garnier told a police interrogator he heard Catherine Campbell's final breaths, and he was haunted by "seeing her, hearing her" gasp for air as he struggled to remember details of the night she died.

"I could hear her take her last breaths," Garnier told RCMP Cpl. Jody Allison on Sept. 16, 2015, hours after the police officer's body was found face down in thick brush near Halifax's Macdonald Bridge.

"I don't know how this happened... I've been trying to remember what happened."

The jury continued to watch the 9.5-hour-long taped interview Wednesday at Garnier's murder trial in Nova Scotia Supreme Court. There's still about an hour and 15 minutes left to watch, and the trial continues Thursday.

Garnier allegedly killed the off-duty Truro, N.S., officer in a McCully Street apartment in the early hours of Sept. 11, 2015, and used a wheeled compost bin to dispose of her body.

For the first roughly five and a half hours of the interrogation, Garnier sat in a grey-clad room sobbing in a computer chair amidst photos of Campbell spread out on a table, telling Allison he wasn't "supposed to say anything."

At one point, Det. Const. Michelle Dooks-Fahie enters the room and takes over the interview, speaking to Garnier in a soft voice.

He repeatedly tells her "I can't" when she asks him to tell her about what happened inside the apartment and "take responsibility."

"This is your time to show it was a mistake, that it happened so fast," said Dooks-Fahie, sitting close to Garnier in a chair, sometimes placing her hand on his shoulder.

Allison re-enters the room.

He tells Garnier he was speaking with investigators and knows what Garnier had in the car when he was arrested.

The jury has heard a tarp, work gloves and rope were among the items found in the car, which was spotted driving by the area where Campbell's body was discovered in the early hours of Sept. 16, 2015. Garnier was arrested minutes later.

Allison says: "Don't tell me she was still alive when you put her in the compost bin."

"No," Garnier replies.

He breaks down and sobs into his hands as he tells the two investigators, "I'm trying to remember."

"She wasn't moving," Garnier said when asked by Allison how he knew Campbell was dead when she was put into the bin. "She wasn't breathing."

Garnier said he remembered being with her in the Halifax Alehouse, where the two had met, but didn't remember who approached who, or going back with her to the McCully apartment.

He told Allison he remembers seeing Campbell bleeding from the nose.

"It's all I can think about. It's why I haven't got any sleep," said Garnier, wearing a T-shirt and pants and sitting with his hands clasped together, the two officers sitting in front of him.

"I remember watching it on the news … I was trying to figure out why the (expletive) I would do something like that. I would never do something like that."

Garnier repeatedly told Allison that he could not remember how Campbell's face became bloody, but eventually said he may have hit her.

"I feel like at this point I'm telling you what you want to hear," said Garnier. "If I knew, I'd tell you. I have no reason to hold anything else back at this point."

He recalled being in the yard of the McCully Street apartment after she stopped breathing, but didn't remember putting her body in the green bin, or walking with it through the city's north end towards the Macdonald Bridge.

But Garnier said he remembered roughly where the body was left.

"When I drove back down there I didn't know exactly where she was," he said, referring to the night of his arrest.

He also said he didn't recall what he did with the mattress.

Garnier earlier told investigators the mattress was stained with blood. Allison drew on the back of a photo, depicting a rectangle representing the bed and a stick figure representing Campbell, her head at the foot of the bed. Garnier drew a circle to indicate where the blood was.

The jury has heard that the mattress has never been recovered.

Dooks-Fahie asked what was upsetting him most.

"Seeing her, hearing her," said Garnier, describing two gasps Campbell made just before she stopped breathing.

Earlier in the interview, a sobbing Garnier told Allison "I'm sorry for what happened" and "I'm not a monster."

When asked what he would say to the Campbell family, Garnier replied: "I'm sorry for what happened."

He also told Allison through tears, "I never wanted anyone to die."

The 30-year-old man has pleaded not guilty to second-degree murder and interfering with a dead body.

Evidence presented at the trial has indicated Campbell was seen kissing and dancing with Garnier at the bar before leaving with him in the early hours of Sept. 11, 2015.

Last week, the defence put forth a hypothetical scenario suggesting Campbell died during a consensual sexual encounter after encouraging Garnier to choke her.