She injected her boyfriend with a lethal dose of heroin. 20 years on, she wants forgiveness.

Twenty years ago, Giuseppe ‘Joe’ Cinque was killed in what has become one of Australia’s most notable and twisted crimes.

His girlfriend, law student Anu Singh, spiked his coffee with Rohypnol before injecting him with a lethal dose of heroin on October 26, 1997.

The chilling story of the death of Joe Cinque. Post continues after post.

She finally called an ambulance 36 hours later, giving paramedics the wrong address for 20 minutes to delay their arrival.

“Could I get an ambulance please? I had a person potentially overdose on heroin,” she told authorities.

“He’s vomiting everywhere blood…Is that a bad sign?”

In the days before her boyfriend's death, Anu had held two dinner parties with her friends in Canberra, telling them she and Joe had made a suicide pact and planned to die together.

But Joe seemingly had no idea about his girlfriend's sick plan.

Twenty years later, after spending four years of a 10-year sentence in prison for manslaughter - she escaped a murder conviction due to "diminished responsibility" - Anu is telling her story in search of forgiveness.

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In a teaser for this week's episode of Sunday Night, Anu, now 44 years old, says she's desperate to "turn back the clock".

"There are many things people don't understand," she tells reporter Steve Pennells in the teaser for the show.

"It's just awful being referred to as a killer, a murderer."

But Joe's parents, Maria and Nino, are still distraught that Anu only spent four years in prison after admitting to authorities she was responsible for killing their son.

"I would ask her, why you really killed him," a teary Maria says in the clip.

"She killed my son. You are the devil. Monster."

Anu will appear on this Sunday's episode of Sunday Night, airing at 8:30pm on Channel 7.