Four males were arrested under terrorism laws on Thursday in connection with the killing of journalist Lyra McKee in Londonderry last month, Northern Ireland’s police force said. McKee, 29, was shot in the head during a riot in the second largest city in the British province on 18 April. The act of violence has since been claimed by dissident republican group the New IRA. “Detectives carried out searches at four houses in the city and arrested four people in connection with the violence which was orchestrated on the streets of Creggan on the evening of Lyra McKee’s murder,” said Police Service of Northern Ireland senior detective Jason Murphy. The four arrested, aged 15, 18, 38 and 51, are being held and questioned in Belfast, police added. The New IRA has apologized over the killing, saying McKee was unintentionally shot as its forces targeted a night-time police raid. A splinter dissident faction, the New IRA seeks the integration of British-ruled Northern Ireland with Ireland — rejecting non-violent political campaigns to achieve unity. McKee established her career writing about so-called “cease-fire babies” — the generation that came of age after the 1998 Good Friday Agreement, which ended the conflict known as “The Troubles.” Her killing evoked memories of those three decades of violence in the province and sparked condemnation across the political spectrum, including in the neighboring Republic of Ireland. Three people — two men aged 18 and 19 and a 57-year-old woman — so far arrested by Northern Irish police in connection with McKee’s killing were all released without charge. Her death follows a recent spate of letter bombings and a car bombing, without fatalities, also claimed by the New IRA. The tempo of fresh attacks has fueled fears that the political turbulence over Brexit — which threatens new border checkpoints on the Irish border — may increase paramilitary activity. McKee’s death has prompted a fresh round of negotiations at Stormont, Northern Ireland’s devolved government, which has been suspended in political deadlock since January 2017. “Lyra symbolized the new Northern Ireland and her tragic death cannot be in vain,” said British secretary of state for Northern Ireland Karen Bradley, announcing the talks last month. The talks began on Tuesday, with parties promising to negotiate in good faith. McKee’s killing also sparked a community backlash against fringe republican paramilitary groups, which regard Londonderry as a historic stronghold. Murals glorifying the armed republican campaign which wound down after the 1998 peace accord were defaced. Meanwhile, friends of the murdered reporter painted blood-red handprints on the headquarters of a political group regarded as the mouthpiece of the New IRA. However, signs appeared last week in the area where McKee was killed warning: “Informers will be shot.”