Eagle-eyed garda spots upskirting offender on the Luas and unearths a more sinister case

Dogged police work brought a sex offender to justice, but the deeper they dug, the more sinister the case became, writes Cormac O'Keeffe

Detective Sergeant Karl Murray witnessed an incident on the Green Line of the Luas that he said made him think 'I can't let this go'.Picture Colin Keegan, Collins Dublin

Karl Murray was off duty when he noticed something odd about a man on the Luas with him.

Both of them had just got on at the  Harcourt Street stop, in Dublin City centre, heading southbound on the Green Line.