As they prowled the In Amenas gas complex for hostages, the gunmen who attacked the Algerian site discovered a brutal but effective tactic to persuade foreign workers to come out of hiding.

They threatened a British man into calling out to his colleagues in English, "Come out, they're not going to kill you", according to an Algerian worker named Chabene who heard the exchange before he escaped.

He said they ordered the man to yell, "They're not going to kill you. They're looking for the Americans". A few minutes later they blew him away."

After the hostage crisis was brought to a bloody end on Saturday by the Algerian military, with the deaths of at least 25 foreigners and Algerians, a picture has begun to emerge of the horror and savagery of the attack.