On 30 January 1972, British troops opened fire on a banned civil rights march through the Bogside area of Derry, killing 13 unarmed civilians.At the end of 2012, the PSNI said they would be opening a murder investigation into the killings.The move followed on from the 12 year, £200m Saville Report which was the longest of its kind in legal history.It found that there was no justification for the shootings and, subsequently, Prime Minister David Cameron apologised for the killings.Now, over 1,000 witnesses, consisting of local people and former soldiers, are being asked by police to make statements as part of the criminal investigation.Detectives want to make contact with - and re-interview - any former soldiers and civilians who gave evidence to the Saville Inquiry or who may have information about the events of 30 January 1972 in which 26 people were shot.A police statement said: "It is necessary to re-interview witnesses because police are precluded from using Saville testimony in a criminal investigation."Civilians and former soldiers are asked to contact the investigation team on 028 9025 9593 or by email to BloodySundayEnquiry@psni.pnn.police.uk"Notices will also be placed in local newspapers and other publications in a bid to encourage witnesses to come forward again.Detective Chief Inspector Ian Harrison, the officer leading the investigation, said: "From the outset we said this would be a lengthy and complicated process and we now have the additional resources in place and a clear investigative process to follow."For the investigation to be as comprehensive and effective as possible, police are asking for public support in the form of witnesses who gave evidence to the Saville Inquiry to now make statements to detectives."He added that contact has also been made with former military witnesses."During the Saville Inquiry it was ruled that anonymity was granted to any former soldier who gave evidence unless his name was clearly already in the public domain. That ruling does not automatically carry over to the current police investigation. Anonymity will be a matter for a future court to consider."Police want to assure all who engage with the investigation team that all matters will be treated in the strictest confidence and the support and welfare of witnesses are important considerations. It is our intention to conduct these inquiries as quickly as possible."