Family, friends and public representatives from North and South of the border will gather in Co. Tyrone later, for the funeral of Ronan Kerr.
The 25 year old PSNI officer was killed last Saturday when a bomb exploded under his car in Omagh.
Thousands of people are expected to turn out for a requiem mass at the Church of the Immaculate Conception in Beragh - among them will be Taoiseach Enda Kenny and the North's first and deputy first ministers, Peter Robinson and Martin McGuinness.
Michael Gallagher's son Aidan died in the Omagh bomb in 1998.
He says walking behind Constable Kerr's coffin is the last thing anyone would want to do......