As the Saville Inquiry enters its final stages after four years of hearing evidence, it has been told it is still unclear which British soldiers shot 27 civilians that day.
The inquiry, chaired by Lord Saville, has been hearing the closing speech by its own counsel, Christopher Clarke.
In his closing statement, Mr Clarke QC said the central question was why and how were civilians killed.
His statement, which is an overview of the issues on which the tribunal's judges must decide, is expected to last two days.
The inquiry is examining events in Derry on 30 January, 1972, when 13 civilians were shot dead by British paratroopers. A final report is expected next summer.