In a video oftwo men amblingby a wharf under sunny skies, a chilling tale emerges.

"How did you?" one man asks the other as they walk toward the end of a wharf at Little Harbour on Gander Lake in central Newfoundland.

The man asking the question — whose face and image are digitally altered — is an undercover RCMP officer.

The man answering the question is Nelson Hart, convicted in March oftwo counts of first-degree murder for killing his twin three-year-old daughters Krista and Karen.

"I said, 'Let's go out and see some fishes.' And that's what they went and done," Hart told the officer, who then joked, "You're going to see them really closely."

The officer, who crouched down at the end of the wharf to mimic the height of the girls, asked Hart to show him what happened.Hart said, "Like this," as he showed how he bumped his body into his daughters.

The bodies of the girlswere pulled from the lake Aug. 4, 2002.

The scene is part of a covertly recorded videotape; one of several played as evidencetoa Newfoundland Supreme Court jury during Hart's murder trial.

The identities of the undercover officers involved in theinvestigation were protected by a court order, so the videos could not be publicly released.

However, CBC News went to court to obtain the videos,on which the officers' facesand voices have been digitally altered. The tapes were released to the CBC last week.

The videos were critical pieces of evidence in the Crown's case against Hart, and came from an RCMP sting that ran for four months in 2005, costing $413,000.

The RCMP launched the undercover operation — involving what's called a "Mr. Big scenario," in which a suspect meets a crime boss and is encouraged to confess to a crime — after investigators hit a dead end in the investigation of the girls' deaths.

Appeal planned

The undercover operation will be an element of the appeal that Derek Hogan, Hart's defence lawyer, is planning to file. Hogan argued that Hart was coerced into making the confession.

Hart originally told police one of the twins fell in the water and that he left the other girl behind while he drove to get help. Months later, he said he had had an epileptic seizure, during which his panicked daughters wound up in Gander Lake.

The videos played for the jury tells a different story.

Hart's re-enactment of the murder at Gander Lake came after a March 2005 confession to an undercover officer in a Montreal hotel room.

Hart had been working for what he believed was a criminal gang for a few months at the time. The gang had promised him a big job, but he was told there was a problem and he had to meet with the top boss of the gang before he could progress any further.

He met with the undercover RCMP officer, whom he thought to be the top boss, in the hotel in Montreal.

'What brought this about?'

During the meeting, the officer asked Hart what happened to his daughters.

"What brought this about? Be honest with me now, what brought this killing your daughters about? Tell me," the officer said.

Hart began to tell the undercover officer the same story he had told police years before, saying, "I had a seizure."

The officer said he didn't buy Hart's story and warned him not to lie.

"You're lying to me on this OK," the officer said.

"That's what I told … that's what I know," Hart replied.

"That's what you told the police,that's the other thing I'm going to ask you. Hey, don't lie to me. Nelson, don't lie to me."

"I wouldn't lie to you, sir."

Thought mother, brother working together

Hart talked about how he felt child welfare and his own family was interfering with him and his daughters. He told the officer he thought his mother and brother were working together against him to take his children away.

"To see a brother raise up my two children — there's no way I could do it, there's no way," Hart said.

Hart also told the officer how he planned to takehis daughters out to the lake that day, saying he had visited the spot before and knew it was a quiet and remote area.

"So you got up that morning and what happened?" The officer asked.

"I got up that morning…. I took the girls out to the park and when they got out of the car I took them out onto the wharf…. I said, 'Let's go look for some fishes.' When they looked for some fishes, that's when I struck them and they went overboard and that's how they drowned."

Hart toldthe undercover officerhe drove back to Gander slowly to make sure the girls would die.

Story changed

He said the police bought his story that he had a seizure and that he hadn't had any trouble with the RCMP for four years.

Hart told police in 2002 that Karen fell into the water, and that he left Krista behind at the lake to get help because he couldn't swim.

But nearly two months after that, Hart changed his story, saying he had a seizure while at the lake. He told police that he initially lied about the seizure because he was afraid officers would take away his driver's licence.

In the Montreal hotel room three years later, the undercover officer asked Hart how he felt about murdering his daughters.

"You ever cry about these girls?" the undercover officer asked Hart.

"Oh yeah.I missed them," Hart said."But how much would I cry to see my brother raise them up? How much would I cry to have them say 'dad' [to him], when I'm their dad?"

Two days after the videotape was made at Gander Lake, police arrested Hart and charged him with the murder of his daughters.