Why did William Maughan and Anastasija Varslavane disappear in 2015?

In April 2015, William Maughan and his pregnant girlfriend Anastasija Varslavane, disappeared without a trace.
The couple, who had been together for about two years were looking forward to the birth of their first child, were planning a move back into Maughan’s family home in Dublin.
But, on the day they were due to move their belongings, they disappeared.
The search for the couple was upgraded to a murder investigation following a review in 2016. And now, gardaí have resumed their search for remains in open lands in north Co Dublin.
What happened to the couple on that spring day in 2015 and might people with information about their disappearance finally come forward?
Presented by Sorcha Pollak, produced by Suzanne Brennan.