Civil rights activists hurl stones in Northern Ireland - and British soldiers fire back.

13 demonstrators were killed on what is known as 'Bloody Sunday' 40 years ago - all were found to have been unarmed.

Families of the victims have campaigned for years and Northern Ireland's police have now announced a murder investigation.

(SOUNDBITE) (English) CHIEF CONSTABLE MATT BAGGOTT, POLICE SERVICE OF NORTHERN IRELAND, SAYING:

"We have an obligation today to keep people safe in 2012, looking forward, but also an obligation, you know, to bring resolution to people who for decades haven't known what has happened and also want to have justice wherever that's possible."

But this member of the British government and former Northern Ireland army officer is uneasy about the move.

(SOUNDBITE) (English) PATRICK MERCER, MEMBER OF PARLIAMENT AND MEMBER OF THE RULING CONSERVATIVE PARTY, SAYING:

"I can understand that their resentment, their grief, burns deep and long. But it's 40 years now - I'm not sure how much this will achieve. Are we really saying that we're going to try and find men in their old age and prosecute them on evidence which, by necessity, is going to be incomplete?"

The so-called ''Troubles'' escalated after these deaths and it wasn't until 1998 that a peace deal was brokered after more than 3,600 had died.

Lily Grimes, Reuters