A film of a woman being beheaded in Mexico caused an international outcry in October when Facebook refused to remove it from its site. There have been hundreds of reports about the video - but why has no-one identified the victim in it?
In the grainy footage, the woman is on her knees in jeans and a pink top, before a masked man holding a knife behind her says in a gruff voice: "Well, gentleman, this is what happens to all those in the Gulf Cartel. On behalf of Los Zetas."
The rest of the video is a gruesome 40 seconds of cold-blooded murder, which caused international controversy recently when it was posted on Facebook.
"Irresponsible" was the word used by the British Prime Minister, David Cameron, about the social network's policy permitting the video to be uploaded. After a day or so of impassioned debate on both sides, Facebook reversed its decision and took the video down.