A silver watch was stolen from the dead body of Sophie Toscan du Plantier in west Cork as a 'trophy' for her killer.
That's according to a leading international journalist, who claims it is a potential breakthrough in the case.
The French filmmaker was brutally beaten to death outside her holiday home in Schull in December 1996.
Almost 25 years later, the case remains unsolved - but Nick Foster, who wrote a book on the case, believes it still can be.
"More witnesses have come forward in Ireland over the last six months, and there's been more leads for Gardaí to investigate.
"I've personally being given tip-offs and I've worked with these people who've shared information with me, so that it reaches the Guards".
One of the tip-offs, he says, is that an object was taken from her body.
"This is really exciting information, potentially a breakthrough - a real breakthrough.
"What I can tell you is this: I recently received a tip-off from the Schull area.
"It's to do with a watch, a silver watch - so a watch of a specific type - that the killer stole from his victim's body immediately after the murder."
Mr Foster wrote a letter to a person of relevance to the case about the new development this week.
He believes it could help to solve the crime.
"I can tell you that I'm very optimistic that there will be progress in the case in Ireland, and ultimately one or more arrests".
Former journalist Ian Bailey was twice arrested in connection with the case, but he has always protested his innocence and was never charged in Ireland.
Speaking back in May, Mr Foster said he was hopeful of 'significant progress' on the case.
He told The Pat Kenny Show: "I think there's an even, or even slightly better chance, that there will be significant progress in the case by - say - the end of the year.
"I am hopeful, I'm exploring some new leads that were passed on to me in the last few months or so.
"The other thing I would say is that allegiances shift over time - so people might come to reflect on their own personal knowledge of the case, and approach Gardaí even at this late stage.
"It's a cold case but it could warm up again - and it certainly should warm up again because Sophie's poor parents deserve closure, as does her son Pierre Louis".