Police are to open a murder inquiry into the Bloody Sunday killings in Northern Ireland 40 years ago.

It follows the Saville Inquiry's report which said civil rights demonstrators shot dead by British soldiers in Londonderry at the height of the Troubles were innocent.

The probe has not started because the resources are not available for the four-year investigation, senior officers said.

Chief constable Matt Baggott said: "It is a matter that I think we should be investigating and will be investigating."

The Police Service of Northern Ireland has consulted prosecution lawyers as it prepares to open a major investigation, which would require a team of 30 and extra specialist help which are not currently available.

Assistant chief constable Drew Harris said: "This will be and is a long and resource-intensive investigation.

"Sustain it we will, but there are some questions we need to bring to the Board in relation to prioritisation of that and other issues in regard to legacy matters."

Thirteen people were shot dead when soldiers opened fire on civil rights marchers on January 30, 1972. Another man died five months later.