Nicole Brown Simpson's sisters discuss domestic violence 30 years after her murder

The sisters of Nicole Brown Simpson have reflected on her devastating murder and the recent death of suspect O.J. Simpson.

Nicole was 35 years old when she was brutally murdered outside her own home on 12 June 1994.

She had been married to American football player O.J. but their seven-year marriage was marred by accusations he was physically and emotionally abusive to her.

Next month marks the 30-year anniversary of Nicole's brutal murder - which is still unsolved. While O.J., who was the primary suspect in the murder but was acquitted of all charges in the criminal trial, died last month aged 76 after battling cancer.

Nicole's sisters, Denise, Dominique and Tanya Brown have been interviewed by ABC News's Diane Sawyer ahead of a new Lifetime documentary, titled The Life & Murder of Nicole Brown Simpson, being released next month.

Asked how they feel about their sister's death all these years later, Tanya said, "It was rough. Unresolved grief. Everything bit me hard ten years later."

Dominique agreed, saying, "Sometimes I would think 'Gosh, I am just staggeringly sad today.' And I would realise that it was the day she was murdered. Or it was her birthday. Or something or some memory would come up."

Denise added, "The pain doesn't go away. It doesn't subside. It doesn't get easier. But you do the best you can and you move on and it's one step forward."

The sisters shared a conflicted view over the fact Nicole's marriage and death changed attitudes to abusive relationships.

Denise questioned, "Why did it have to take my sister? Why did it have to take Nicole for people to understand that domestic violence can kill?"

When asked if the death of O.J. has impacted them, Dominique said, "It's very confusing. It's very complicated. But I have a relationship with the kids that means everything to me and I was just very, very sad for them."