By Peter Griffiths
LONDON (Reuters) - Police in Northern Ireland said on Sunday they plan to question witnesses to the killing by British soldiers of 13 Roman Catholic civil rights marchers in Northern Ireland 40 years ago.
The interviews form part of a murder investigation announced by the police in 2012 in relation to the "Bloody Sunday" killings, one of the most notorious episodes during 30 years of sectarian violence in the British-ruled province.
On Sunday, January 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.
"Preliminary work has begun into what will be a lengthy and complex investigation," the Police Service of Northern Ireland said. "For the investigation to be as comprehensive and effective as possible, police will be asking for public support in the form of witnesses who gave evidence to the Saville Inquiry now making statements to detectives."
That inquiry by High Court judge Lord Saville was the longest and most expensive in British legal history.
It concluded in 2010 that there was no justification for the shootings, prompting Prime Minister David Cameron to apologize for the killings.
Citing an unnamed source close to the police, the Sunday Times newspaper said up to 20 retired British soldiers could be arrested on suspicion of murder or attempted murder.
A spokesman for Britain's Ministry of Defence declined to comment.
The 1972 killings boosted support for the Irish Republican Army, allowing it to intensify its violent campaign for Northern Ireland to secede from the United Kingdom and become part of the Republic of Ireland.
A 1998 peace deal has largely ended the violence in Northern Ireland and Londonderry, Northern Ireland's second city, has enjoyed a strong revival.
(Additional reporting by Padraic Halpin in Dublin; Editing by Alistair Lyon)