DUBLIN — Officials in Northern Ireland said on Thursday that one former British soldier would be prosecuted on murder charges in connection with the massacre of unarmed civilians by British forces nearly 50 years ago in Londonderry, an event that came to be known as Bloody Sunday.

The former soldier, identified only as “Soldier F,” will be charged in the killings of James Wray and William McKinney, and with the attempted murder of four others. Eighteen others, including 16 former British soldiers and two nationalist gunmen said to have fired shots that day, will not be prosecuted, the officials said, on the grounds that there was insufficient evidence to provide a reasonable chance of conviction.

The massacre on Jan. 30, 1972, became one of the main flash points in the Troubles, the 30-year struggle over the status of Northern Ireland that claimed at least 3,500 lives.

[The Troubles still cast a shadow over Northern Ireland.]

The announcement in Londonderry on Thursday by the Public Prosecution Service of Northern Ireland was greeted with dismay by many of the victims’ families, some of whom said they would mount a legal challenge.