How the weather can play a vital part in catching a killer

Text messages, website interaction, files recovered from computer laptops, and CCTV footage were vital in the prosecution's case.

Now, winding the clock back, prior to all that evidence being uncovered by numerous detectives, it was a twist of fate that brought Dwyer to the attention of the gardaí in the first place.

The summer of 2013 was a great one in that we all enjoyed dry and warm weather. Hidden in the depths of the water at Vartry Reservoir, near Roundwood, Co Wicklow, were numerous items belonging to Ms O'Hara, which were significant to the case. Our good spell of weather meant the water level dropped dramatically, allowing those items to be recovered, which helped to unlock the mystery of the childcare worker's disappearance.

Credit must go the anglers who noticed these items and to Garda James O'Donoghue, who returned more than once to the reservoir to search for and find more clues. These pieces of evidence and the discovery of Elaine's body, within days of each other, allowed the investigative team to connect Dwyer and O'Hara, in what up until then had been a 'missing persons' case.

This recent trial brought me back to the case of Marilyn Rynn and how the weather also played a huge part in capturing her killer almost 20 years ago. Marilyn was 41, living in Blanchardstown, Dublin, and working in the Department of the Environment. Enjoying a Christmas night out with her co-workers on December 21, 1995, she disappeared later that night after taking the Nitelink bus home. My birthday falls the next day so I think this is one of the main reasons her story has always stayed with me, and each year I am reminded of her. Sadly, Marilyn's body was found in early January 1996 at Tolka Valley Park. She had been viciously assaulted and murdered. The man eventually found guilty of the crime, David Lawler, actually incriminated himself. Senior gardaí established that he had checked the internet to find out details on how long body fluids could survive at the scene before degrading.

Apparently satisfied that all fluids would have been destroyed before Ms Rynn was found, Lawler provided a genetic fingerprint.

By total coincidence, what he had not considered was just how cold that winter had been. Below-zero temperatures had frozen the body, the DNA was still intact, and Lawler was found guilty of the crime.

December was also the month of the horrific disappearance of Jean McConville in west Belfast.

The mother of 10 was taken from her home by the IRA in 1972, and she was never seen again.

After just over 30 years of searching, her body was found in 2003.

Her remains were only discovered after heavy rains dislodged them from Shelling Hill beach on the Cooley Peninsula in Co Louth. We still don't know all the details of what happened to Mrs McConville. However, I hope the recovery of her body has brought some solace to her family, allowing them to bring her home, and bury her where they wish.

So, there is no such thing as the perfect murder. It is near impossible to contain all the elements that can potentially provide clues to solve any case.

I, for one, am relieved that while sometimes Mother Nature is the silent witness to crimes, eventually she wants to be heard, and brings key evidence to our attention.

Nuala Carey reads the weather on RTÉ