They must have had a tip off, either now or 4 years ago when they upgraded it to a murder case. I read on X that the person who gave him an alibi at the time and for the past 29 years, has recently retracted it, maybe they have been negotiating with that person for the past 4 years, and he possibly had more information that he disclosed.
Anyone remember the guy in Youghal, who claimed his wife just upped and left out of the blue and didn't report her missing, it was her sisters who reported her missing, then he 'found' her suitcase at the dump. Always on TV doing appeals for his wife, was as clear as day to everyone that he was behind her disappearance, her family knew he murdered her, but yet the gardai appeared to have never properly searched their house, and the poor guys doing drains a few years later on the road found human remains, which led the gardai to finally do a proper search of the house and found her remains behind a wall he had built soon after she disappeared. . I mean you have to wonder is it incompetence of the investigating Gardai, or do they just not give a shit because it is a woman, or are their hands tied with protocol and bureaucracy that they really can't move forward for fear of getting wrong.