One morning in November 1985, an RAF airman out for a run on an Anglesey beach found a man’s body washed up on the shore.

A quirk of the tide means that an unusually high number of bodies have washed up on beaches in north Wales over the years. This one had distinctive scarring and did not match descriptions of any missing person at the time. Despite an extensive investigation, police failed to identify him. The case was dropped and the remains were buried in an unmarked grave.

Just over 30 years later, in 2016, Alan Dowley, a retired police officer in the Republic of Ireland, contacted north Wales police. His father, Joseph Brendan Dowley, was last been seen by his family on 17 October 1985, when his daughter dropped him off at the MacDonagh bus station in Kilkenny. The 63-year-old had been due to catch a ferry across to England and then travel to London where he lived and worked.

When the family didn’t hear from him for two months, Alan Dowley started to make inquiries. “I checked with his bank and there was no activity on the account,” he said. “I checked with the department of health and social welfare in London and there was no activity. Then we checked his last known address and he hadn’t been seen there for some time. It was at that stage that I reported him missing.”

Joseph Brendan Dowley disappeared aged 63. Photograph: North Wales police

Over the years, Dowley, now 65, had done investigative work of his own and had obtained his father’s medical records from St Mary’s hospital in London. The records showed that his father had scars from a hernia operation that was not known about at the time of the disappearance. The scars matched thoseon the body found in 1985.

On 19 June this year, the remains were exhumed from Menai Bridge cemetery for DNA testing, and last month, after 33 years, the body was formally identified as Joseph Brendan Dowley. His remains were repatriated to Ireland on 28 August.

The discovery was the result of parallel police investigations by North Wales police and the Gardaí in Ireland to identify the comparatively high number of bodies washed up on beaches in north Wales, many of which are thought to come from Ireland.

“Wales has got a lot of coastline, so we seem to get a disproportionate amount of coastal finds [bodies washing up on beaches],” said DS Don Kenyon, who is leading the North Wales police operation. “The way the tidal floods work in the area, Anglesey and Llŷn peninsula get in the way and people end up washed up on the beaches for that reason.”

“On the eastern seaboard, from Dublin as far as Waterford, the way the current will work is that it generally pushes bodies towards north Wales,” said Richard Lynch, from the Gardaí missing persons unit. “If people go in off the western seaboard and the current takes them, we’d do well to get them back unfortunately, just because there’s 3,000 miles of ocean between ourselves and America.”

Operation Orchid, established by North Wales police in 2010, was tasked with naming the 16 unidentifiedbodies buried in the region between 1968 and 2002; 11 of these were discovered either in the sea or on the coastline. (There are currently 926 unidentified bodies or body parts on the UK missing persons database, dating from 1950.) DNA was first used by police for identification purposes in 1986, and the operation uses modern forensic science that was not readily available at the time the bodies were discovered.

Operation Runabay was launched by the Gardaí missing persons unit in January 2017 to identify bodies found on the western coast of Great Britain who may have been reported missing in Ireland. There are 120 cases outstanding.

As well as Joseph Dowley, Operation Orchid has also successfully identified the body of Pauline Finlay, who disappeared while walking her dogs on a beach in Kilmuckridge, Co Wexford, on 25 March, 1994. Leg and hip remains were found at Cable Bay in Holyhead seven months after her disappearance, but were only formally identified in 2016. Her husband Joe died before getting the chance to attend her funeral.

Among the other cases being investigated is that of a woman’s body found in the sea off Barmouth on 28 June 1978. She is described as 5ft 6in, of medium build, and was found wearing a blue swimsuit from St Michael, the Marks and Spencer brand.

In another case, the body of a man believed to be 25 to 30 years old was found in the sea off Holyhead on 30 May 1982. He was between 6ft and 6ft 2in with short black hair and a stocky build. The body had been in the sea about a month and was dressed in outdoor clothing, including a blue Berghaus jacket, a blue Santa Fe anorak, brown calf length boots and red socks.

He was found with a rucksack decorated with “Ponderosa camp trail” badges. The original police file states that the man may be Irish, but there is no information about why officers came to this conclusion.

Another man, believed to be between 55 and 60 years old, was found on the beach in Aberdovey on 28 December 1982. He was around 5ft 10in, of medium build, had a surgical scar on his neck and a complete set of upper dentures. He was wearing a Richard Davies shirt manufactured by JC McMullan Ltd of John St, Dublin. Apart from one consignment to Aberdeen in December 1982, the shirts were only distributed in Ireland.

For Ann Ellis from the Gardaí missing persons unit, the cases do not lose importance as time goes by. “They are someone’s family member and these questions have been open for years on end,” she said. “If we can give these families any indication that we haven’t forgotten and that we are still trying to find answers for people, that’s very important.”

Alan Dowley said he believed his father had either fallen or jumped off the ferry to England, but accepted that the exact circumstances of his death would remain a mystery. “It’s different if someone has gone missing in the last few weeks and then the body is discovered,” he said. “That’s a shock. But we’ve had 30 years to deal with this. Alright, you may never know exactly what happened, but you accept that they are gone and you just have to move on with your life.”