A 66-year-old former soldier has been arrested in connection with the killing by British forces of 14 Catholic civil rights marchers in Northern Ireland over 40 years ago, Northern Irish police said Tuesday.

The arrest is the first in a renewed murder investigation announced by police in 2012 into the “Bloody Sunday” killings in Londonderry, one of the most notorious episodes during 30 years of sectarian violence in the British-ruled province.

The questioning “marked a new phase in the overall investigation which could continue for some time,” the officer leading the probe, Detective Chief Inspector Ian Harrison, said in a statement.

Britain’s Ministry of Defense said it was aware an ex-soldier had been arrested in connection with the investigation and that it would be inappropriate to comment further.

On Sunday, Jan. 30, 1972, British troops opened fire during an unauthorized march in the Bogside, a nationalist area of Londonderry. They killed 13 people and wounded 14, one of whom died later. The victims were all unarmed Catholics.

A 2010 inquiry — the longest and most expensive in British legal history — concluded that the civilians had been killed without justification and had posed no threat, prompting Prime Minister David Cameron to apologize for the killings.

Soldiers who gave evidence to the inquiry about their involvement did so from behind screens and with a guarantee of anonymity.

The killings changed the course of the violent “Troubles” that erupted in the late 1960s, boosting the Irish Republican Army's violent campaign for Northern Ireland to secede from the United Kingdom and become part of the Republic of Ireland.

A 1998 peace deal, brokered after more than 3,600 had died, has largely ended the conflict that pitted mostly Catholics, who wanted a united Ireland, against Unionists, mostly Protestants, who wanted it to remain part of the United Kingdom.

Reuters