DUBLIN (AP) — Northern Ireland’s police commander says he doesn’t have the resources to start investigating the Bloody Sunday massacre to determine whether any British soldiers should be charged with murder.

Families of the 13 people killed when troops opened fire on Irish Catholic demonstrators on Jan. 30, 1972, have waited for a criminal investigation to start since 2010, when the biggest fact-finding probe in British history determined that the soldiers targeted unarmed civilians.

Chief Constable Matt Baggott told Northern Ireland’s policing board Thursday that his force is planning a Bloody Sunday investigation that would require 30 detectives and take four years. But he said his force doesn’t have enough staff or funding to start.

British soldiers killed 309 people in Northern Ireland from 1969 to 1996, more than half of them civilians.