Timeline of terror over the past year
March 4, 2016
Prison officer Adrian Ismay is seriously injured after a booby-trap bomb explodes underneath his van in east Belfast.
The 52-year-old died 11 days later from injuries sustained in the attack.
October 16, 2015
A "military-style hand grenade" is thrown at a patrol in east Belfast as officers respond to reports of anti-social behaviour near Pottingers Quay.
The device failed to explode.
October 15, 2015
A bomb is found at Linden Gardens, off the Cliftonville Road in north Belfast. Police said it may have fallen from a car belonging to a man with connections to the armed forces.
October 10, 2015
A bomb is found in the grounds of a Londonderry hotel ahead of a police recruitment event. The event was cancelled. Two other recruitment events in Belfast and Omagh went ahead despite bomb alerts at the venues.
August 1, 2015
A mortar bomb is found in a graveyard in Strabane, Co Tyrone, in a location where it could have been used to kill officers.
The device was positioned where it could be used to attack passing PSNI patrols, police said.
June 18, 2015
A booby-trap bomb is found under a police officer's car in Eglinton, close to Derry, on June 18.
Police said the attack was a "clear attempt to murder police officers".