“I am quite confident that somebody out there has information which, for whatever reason, they decided to keep to themselves,” Det Ch Insp Davies said.
“Three decades have passed – that person may now be in different circumstances. It is never too late to come forward.”
Ms Jones’ sister Mary said the family had “never stopped living the nightmare” of losing their loved ones.
“In October 1995 my heart, my life got shattered into a million pieces,” she said.
“We didn’t just lose a sister and our nieces, we also lost our parents. It absolutely broke their hearts.”