(CNN) -- Authorities hunting the killer of a police officer in Northern Ireland last week say they have seized a gun and ammunition.
Two people in masks prepare to throw petrol bombs in Lurgan, Northern Ireland.
They were found Saturday in Craigavon, the town where Stephen Carroll, 48, was shot dead on Monday, a police statement said Sunday.
Authorities also arrested two more people in connection with the killing of Carroll -- a 37-year-old man and a 30-year-old woman. That brings the total in custody to five, police told CNN.
And they arrested another person over the killing of two soldiers just days before Carroll was killed. A total of four people are now in custody in the killing of soldiers Cengiz "Pat" Azimkar, 21, and Mark Quinsey, 23, at the Massereene barracks March 7.
The Massereene barracks killings were the first fatal attack on British troops in the province for more than 12 years. Carroll was the first police officer killed in political violence since 1998.
The shootings have raised fears that the province could plunge back to the sectarian violence that claimed the lives of 3,600 people over three decades before the Good Friday Agreement in 1998.
The Continuity IRA, a republican splinter group that does not accept the Good Friday Agreement, said it had killed Carroll, while the Real IRA, another splinter group, said it had killed the soldiers, Britain's Press Association reported.
Northern Ireland's top police officer, Hugh Orde, insisted Sunday that the militant groups that want the province to leave the United Kingdom and become part of Ireland are "small ... disrupted, infiltrated and disorganized."
"The current wisdom is that they number around 300 in a population of 1.75 million," he wrote in Britain's News of the World newspaper.
But, he said: "In the past 18 months or so there have been at least 25 attempts by dissident terrorists to kill officers on and off duty."
Rioting flared near Belfast, the capital of Northern Ireland, after an earlier round of arrests Saturday.
Police said petrol bombs were hurled at police in Lurgan, west of Belfast. There were no arrests or injuries reported, despite gangs of youths on the streets, authorities said.
One of the men arrested in connection with the killing of the soldiers, Colin Duffy, 41, is from Lurgan. He was among three whose arrests were announced Saturday.
A fourth man was arrested Saturday night, said the police spokeswoman, who declined to be named in line with policy. She released no details about the man or the location of the arrest.
The two British soldiers were shot dead a week ago at a base in Massereene, in Antrim, as they were preparing to ship out for duty in Afghanistan.
The soldiers had packed their bags and changed into their uniforms, authorities said.
Two masked gunmen with automatic rifles shot them as the soldiers picked up a pizza delivery at the barracks, authorities said. Two other soldiers and the two pizza delivery men were seriously wounded.
Politicians from across the political spectrum have condemned the killings, with Sinn Fein deputy leader Martin McGuinness calling the killers "traitors to the island of Ireland."
Sinn Fein is a predominantly Catholic party that wants Northern Ireland to leave the United Kingdom and become part of the Republic of Ireland. The party is widely thought to be linked to the Irish Republican Army.
Danny Kennedy, deputy leader of the loyalist Ulster Unionist Party, which wants Northern Ireland to remain part of the United Kingdom, also condemned the attack as "wicked and murderous."
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