The Secret Policemen
Secrecy for Catholic police officers in Northern Ireland can be the difference between life and death.
For decades most Catholics were suspicious of the police - because the force was overwhelmingly Protestant and seen as enforcing British rule.
Political agreement in Northern Ireland revolutionised policing.
The police force became a police service, made more representative by the adoption of neutral symbols and by a recruitment programme designed to increase the numbers of Catholic officers.
Constable Ronan Kerr was one of that new generation of recruits.
A Catholic officer from a nationalist family, he was killed by a bomb which exploded under his car on the 2 of April 2011.
He was 25 years of age and had been a serving officer for a matter of months.
His killers are dissidents who oppose the political settlement and who view any Catholic and nationalist who joins up as a traitor.
Catholic members of the PSNI must be extremely careful about who they tell about their job - sometimes even having to lie to family and friends.
Barbara Collins investigates the toll taken by this life of secrecy.
(Image: A heavily armed PSNI (Police Service of Northern Ireland) police officer on patrol. Credit: Press Association)