Nicole Brown Simpson's 30-year death anniversary is coming up -- with her sisters saying they're still battling grief ... and O.J. Simpson's passing hasn't helped them move on.
Denise, Dominique and Tanya Brown sat for an interview with Diane Sawyer ahead of a new documentary that's coming out that looks back on Nicole's life and murder -- which they believe was carried out at the hands of O.J. ... even though he was criminally acquitted.
Despite that, the Brown siblings say there were warning signs in Nicole and O.