DERRY, Northern Ireland — On a cold, rainy night last January, a group of masked men abducted a 15-year-old boy from his home in Creggan, Northern Ireland, threw him into the back of a van and took him to a dark alleyway. There, they pinned him against a shuttered storefront and shot him in the legs until he collapsed.

The men were linked to one of the region’s main militant groups, the New Irish Republican Army. “They beat me up, I couldn’t breathe and then bang, bang, bang, bang. Everything went blurry and I fell to the ground,” the teenager, now 16, recalled, speaking on the condition of anonymity out of fear for his safety.

“Two of the bullets hit me directly in the shins and two more pierced my thighs. The blood was just pouring out everywhere,” he said, rolling up his tracksuit to reveal the bullet wounds, which have left two crevasses under his kneecaps.

Violence in Northern Ireland has fallen sharply since the 1998 Good Friday agreement formally ended a bloody 30-year guerrilla war between mostly Catholic republicans, seeking unification with the Republic of Ireland, and predominantly Protestant loyalists and unionists, who favor remaining in the United Kingdom.