'I Think He Drowned': Dramatic 911 Call Reveals New Details in New York Kayak Murder Case Angelika Graswald is accused of intentionally killing fiance Vincent Viafore.

 -- A tape of the 911 call obtained by ABC News’ “20/20” reveals how Angelika Graswald, the woman accused of intentionally killing her fiancé while kayaking in the Hudson River, appeared to have reacted as he drowned.

Graswald, 35, called 911 on April 19, saying that she and her fiancé Vincent Viafore, 46, had been out kayaking on the Hudson River when his kayak flipped over and she wasn’t able to reach him.

“Oh my God. I'm in a red kayak, but he fell in, I couldn't swim to him. I couldn't paddle to him,” Graswald is heard telling the 911 operator. “He's getting farther and farther away from me. He's going to drown. Please call somebody.”

Graswald told the 911 operator that high winds and waves prevented her from getting to him.

“He has something that he's holding onto, but it's getting very bad. The waves are very strong, I can still see his head,” Graswald said during the 15-minute call.

Then, before the call ends, Graswald says, “I think he drowned, I need him to be rescued.”

Viafore’s body was found in the Hudson River near the United States Military Academy at West Point about a month later on May 23. The Orange County, New York, medical examiner ruled Viafore's death by drowning, according to the autopsy report, a copy of which was obtained by ABC News.

There is controversy surrounding the medical examiner’s conclusion that Viafore’s death was a homicide by a “kayak drain plug intentionally removed by other.” Graswald’s attorney has disputed these findings, saying it was based on investigators’ speculation. And experts tell ABC News a missing drain plug would not cause a kayak to sink, even in rough water.

Graswald, a Latvian national, initially told authorities that she fell out of her kayak while trying to help her fiancé, then was found by a boater and rescued, police said. Police noted at the time of the incident that Graswald was treated for hypothermia at a local hospital and released.

Then, prosecutors said in April that Graswald admitted to investigators that she had tampered with Viafore's kayak and paddle. Prosecutors said at the time Graswald also told police that she watched Viafore struggle in the Hudson's icy waters for several minutes before he went under, and that it "felt good knowing that he was going to die," implying that "this was her only way out."

"It is also alleged that she moved the paddle away from him as he was struggling to stay afloat with water temperatures in the 40 degree range, and failed to render him assistance including timely calls for help," the Orange County, New York, District Attorney's office said in a news release in May.

Graswald was indicted on second-degree murder charges and second-degree manslaughter charges in May. She has pleaded not guilty, and her bail is set at $3 million in cash or $9 million bond. She is due in court next on Oct. 16.

The second-degree murder charge in the indictment carries a potential penalty of as many as 25 years to life.

ABC News' Lisa Soloway, Brooke Stangeland and Emily Shapiro contributed to this report.