© APPallbearers carry one of 13 coffins of Bloody Sunday victims after the requiem mass at St Mary's church at Creggan Hill in 1972
Up to 30 officers will investigate 1972 massacre, in what the brother of a victim called a step in the right direction

Northern Ireland's chief constable, Matt Baggott, has confirmed that his officers would be conducting a murder inquiry into the army's killing of 13 civilians on Bloody Sunday 40 years ago.

Up to 30 officers are expected to join the inquiry team, although the head of the Police Service of Northern Ireland was unable to say when the inquiry would begin.

Some of the families of the Bloody Sunday dead have called for members of the Parachute Regiment involved in the 1972 massacre - one of the biggest atrocities of the Troubles - to be arrested and face prosecutions over the shootings.

Baggott told the Northern Ireland Policing Board on Thursday: "It is a matter that I think we should be investigating and will be investigating." His assistant chief constable, Drew Harris, added: "That will be a large investigation obviously and setting aside the resources to properly start that and take that forward is a corporate issue which is under investigation at this time." John Kelly, whose brother Michael was shot dead on Bloody Sunday, said: "It certainly is good news, but it was something we were expecting anyway. My view on it at the time was these soldiers should have been arrested straight away and prosecuted on what came out of the Saville report. But certainly after hearing what we heard today it's a step in the right direction because myself, my family and most of the families want prosecutions."

Unionists called for Martin McGuinness, Northern Ireland's deputy first minister, to be questioned by police over his role in the IRA on Bloody Sunday.

McGuinness admitted during testimony to the Saville tribunal, which investigated the massacre, that he was the IRA's second-in-command in the city on the day of the shootings.

The Ulster Unionist party's justice spokesman, Tom Elliot, said the decision proved there was a "hierarchy of victims" in Northern Ireland.

"Those whose loved ones died at the hands of terrorists and who have been denied such an inquiry are not being afforded equality," Elliot said. The UUP spokesman and former party leader said that if prosecutors were going to conduct a murder investigation based on Saville, he could "only assume they will also be seeking to question Martin McGuinness regarding the findings of that same inquiry that he was armed on Bloody Sunday. And if [they're] not, why not?"

Elliot said unionists would be shocked to learn that the PSNI had set up the murder team given the number of other unsolved crimes of the Troubles.

The Saville Report concluded that none of the 13 people shot dead (a 14th died later) were armed and that all were innocent victims - a verdict wholly accepted by David Cameron in his speech officially launching the report in 2010. The prime minister issued an apology in the Commons describing what happened as "both unjustified and unjustifiable".

It is unlikely that any former member of the army involved in the killings in Derry would serve long jail sentences given that under the Good Friday agreement, all crimes committed prior to 1998 have a de facto amnesty. It resulted in the early release of IRA, INLA and loyalist paramilitary prisoners, including convicted murderers from the Maze prison, as part of the peace deal.

Bloody Sunday occurred on 30 January 1972 after a civil rights march to protest against ongoing internment without trial. The Saville inquiry began in 1998 and cost £195m, making it the most expensive inquiry in British legal history.