Woman accused of drowning her fiance made chilling confession, court hears.

Angelika Graswald confessed to deliberately sabotaging her fiance’s kayak knowing he would drown in the icy waters below, according to chilling new testimony.

A New York police investigator has publicly described for the first time a 45-minute walk he took with 36-year-old Graswald that led her to be charged with killing her fiance Vincent Viafore.

Viafore, 46, disappeared in the Hudson River’s rough, cold waters on April 19, 2015, while visiting Bannerman Island with his then future bride. The couple had paddled to the island where they spent the day drinking beer and taking photos before Viafore vanished on the return trip.

Investigator Donald DeQuarto testified Graswald removed the plug from Viafore’s kayak, ensuring it would capsize, and snatched away his paddle, New York Times reports.

DeQuarto said that Viafore begged Graswald to call 911 as he floundered in the choppy waters without a life vest, but she “kind of reached over and took his paddle from him and strapped it onto her kayak.”

Asked if she removed the plug so he would drown, she allegedly paused before admitting, “I guess I did”.

His testimony comes on the fourth day of a pre-trial hearing to assess how investigators obtained their evidence against Graswald.

Graswald was treated as a mourning fiancee for 10 days while divers searched for Viafore's body until detectives took her to the island and DeQuarto had a lengthy, one-on-one conversation with her. The next day, she was interrogated by police for 11 hours.

When DeQuarto asked how she felt about Viafore's death, she allegedly said: "Fine. Over It."

"She felt like herself. She felt free," he said.

Woman charged in kayak death admitted keeping paddle from fiancé, officer testifies https://t.co/BB8eHRrQnh pic.twitter.com/GujCpZJ77Z

— The New York Times (@nytimes) June 21, 2016

He told the court he discovered Viafore had postponed their wedding and made unwanted sexual demands, forcing her to have sex when he wanted to and pressing her to have threesomes.

Graswald allegedly said Viafore even had a third partner in mind, named Tina.

“‘Why can’t you do a threesome with Tina? Tina would do this, Tina would do that.’ It made her upset,” DeQuarto said.

DeQuarto testified that Graswald told him she felt Viafore had "trapped" her, People reports.

"I just wanted to be free. I wanted him gone, I wanted to be myself," he recalled her telling him.

DeQuarto said he had asked Graswald why she didn’t just break up with Viafore.

He claimed “she said she’s a very spiritual person, she knew he would never be gone” if she only dumped him.

DeQuarto said Graswald suggested she could have pictured herself remaining with Viafore if things had been different.

“She wanted a normal life with Vincent, she wanted to get married, she wanted to have children,” he said.

DeQuarto didn't take notes nor did he record the conversation he had with Graswald on the island. He only wrote down his memory of the talk 15 hours later. He also did not tell Graswald she had a right to remain silent.

Graswald's defence lawyer is challenging how police obtained statements leading to her arrest and is seeking to suppress an 11-hour interrogation video, which shows an alleged confession.

Graswald is rejecting her charge of second-degree murder, maintaining Viafore died accidentally when his kayak capsized and he fell into the water.

Prosecutors say Graswald stood to collect US$250,000 in life insurance benefits from Viafore's death. His body was recovered in mid-May last year.