LONDON — Relatives of victims of Northern Ireland’s deadliest bombing are suing the police over alleged failings they say allowed the killers to escape justice.

Families belonging to the Omagh Support and Self Help Group have issued a writ against George Hamilton, chief constable of the Police Service of Northern Ireland.

A car bomb planted by IRA dissidents exploded amid shoppers, workers and tourists in the town of Omagh on Aug. 15, 1998, killing 29 people.

After several failed prosecutions, no one has been convicted in a criminal court of the attack, the deadliest single bombing in Northern Ireland’s three decades of violence.

Michael Gallagher, whose 21-year-old son Aiden died in the bombing, said Thursday that “we are 19 years on and the criminals responsible for this are still walking the streets.”