American woman Heather Mack has made a shocking confession on YouTube claiming that she acted alone in the grisly killing of her mother in Bali.

The 21-year-old, who was convicted in 2015 for her role in helping murder her mother with her then-boyfriend, Tommy Schaefer, posted a series of three videos on YouTube titled "Confession" on February 2.

Mack, from Chicago, was sentenced to 10 years in jail after she and Schaefer were found guilty of murdering the wealthy widow at a luxury Bali hotel and stuffing her body in a suitcase in August 2014.

In the video, Mack starts out by saying "the truth sets you free" and says she "doesn't want to live in a lie anymore".

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Mack then admits she hatched a revenge plot to kill her mother, Sheila von Wiese-Mack, as payback for her mother killing her father when she was a child.

"When I was 10, my mother killed my father in a hotel in Athens, Greece. Two weeks before I came to Bali, I found out that she killed my father and I made it up in my heart, in my mind, in my soul, in my blood, in the oxygen running through my body that I wanted to kill my mother," she said in the video.

Mack was 10 when her father, acclaimed jazz composer James L. Mack, died of a pulmonary embolism during a family vacation in Greece in 2006, according to his obituary.

"First I asked Tommy Schaefer to find somebody to help me kill my Mum for $50,000. He said no. After that, I got this new savage idea in my head that I wanted to kill her in a hotel room, because she killed my father in a hotel room," Mack said.

"We were going to Bali so I began to plot."

At the trial, Schaefer testified that he delivered the fatal blow to Ms von Wiese-Mack with a metal handle of a fruit bowl.

However, Mack has now claimed this was all part of the attempted cover-up, expressing remorse for entrapping him into that role.

According to The Chicago Tribune, Debbie Curran, who is the younger sister of von Wiese-Mack, called Heather's claims "completely false".

"Heather Mack's stories about her relationship with her mother and the events in Bali have changed so many times, it is impossible to discern truth from deception," she reportedly told the Tribune in a written statement.

"However, her accusation about Sheila killing Jim is completely false. Sheila loved Jim very deeply and was devastated by his death."

Mack gave birth to a healthy girl named Stella in March 2015 and is raising her in prison, per local custom, until she turns 2 next month.