The first police witnesses are giving evidence to the Bloody Sunday Inquiry in Londonderry.

The inquiry in the city's Guildhall is examining the events of 30 January 1972 when 13 civilians were shot dead by British Army soldiers during a civil rights march. A 14th person died later.

Heavy security surrounded the building on Monday as the tribunal heard the testimony of retired RUC Special Branch officer William George Hunter.

Mr Hunter is giving evidence screened from the public by a wooden booth - but not the inquiry judges and lawyers.

The tribunal ruled that he faced a "special danger" which overrode the public duty to conduct an open inquiry.

Inquiry chairman Lord Saville is hearing police evidence

He told the tribunal that he was at William Street behind Army lines on Bloody Sunday looking for known republicans at the march.

Mr Hunter said he heard at least 10 nail bombs being thrown and a Thompson machine firing before the Army opened fire.

The Thompson model was a type used by the IRA at the time.

Soldiers involved in Bloody Sunday have always said they were fired on by the IRA before they opened fire.

However, this has been denied by former IRA members and civilian witnesses.

Mr Hunter said he did not spot any terrorist suspects taking part in the march.

More former and serving police officers are to give evidence over the next two weeks.

Some police officers will give evidence unscreened.

The beginning of police evidence marks a new phase in the inquiry following more than a year of civilian testimonies.

The inquiry was adjourned last Tuesday during commemorative events in Londonderry to mark the 30th anniversary of the killings and resumed on Monday morning.

Establishing facts

Lord Saville of Newdigate and the Commonwealth judges accompanying him on the Bloody Sunday Inquiry began their work nearly four years ago.

They are not expected to report back until 2004, by which time the costs are likely to have exceeded �100m.

The Bloody Sunday inquiry was established in 1998 by Prime Minister Tony Blair after a campaign by families of those killed and injured.

They felt that the Widgery Inquiry, held shortly after the shootings, did not find out the truth about what happened on Bloody Sunday.

Witnesses to the inquiry are immune from prosecution on issues arising from their evidence. It is aimed solely at establishing the facts about what happened.