I'd almost forgotten about More 4 and happened to see this listed.
Drama based on true events. Three young women go missing from the Perth suburb of Claremont in the mid-90s.
The mystery takes police decades to solve.
https://www.channel4.com/programmes/the-claremont-murders
It doesn't seem available to watch online - but maybe later.
Also, as I got caught out by this with another series, each episode is 2 hours long.
I didn't read too much as I didn't want to see any spoilers but seems to have had good reviews from when first shown on Acorn TV.