BBC documentary highlights violence committed by undercover British Army unit in 1970s Belfast

A BBC documentary on an undercover British Army unit that killed civilians in Belfast in the early 1970s has raised new questions about the limits of prosecuting people for Northern Ireland's bloody past.

Thursday's broadcast shows former members of the disbanded Military Reaction Force describing their involvement in illegal shootings and boasting that their mission was to terrorize Irish Republican Army members and supporters. A clandestine 40-member MRF unit operated in Irish Catholic parts of Belfast from 1971 to 1973, the deadliest years of conflict.

The documentary comes one day after Northern Ireland's attorney general called for all investigations to be halted into killings committed before the Good Friday peace accord of 1998.

A report published Thursday estimated the future cost of such investigations at 190 million pounds ($305 million).