It was as chilling as it was deliberate. Determined to flush out any Westerners hiding amid the sprawling complex of the Tigantourine gas plant, the gunman turned his weapon on his British captive.
He then forced him to call out to his colleagues, luring them from where they were sheltering. Moments later, his purpose served, the unnamed engineer was shot dead.
An Algerian cook named Chabane, who had managed to hide after jumping out of a window during the confusion of the attack, witnessed the treatment of the Briton.
"They threatened him until he called out in English to his friends, telling them, 'Come out, come out. They're not going to kill you. They're looking for the Americans,'" he said. "A few minutes later, they blew him away."
The account emerged as rescued hostages and Algerian officials told how members of the Masked Brigade, also known as Witnesses in Blood – a splinter group of al-Qa'ida – attacked the gas complex early on Wednesday.
Instead of passing through Algeria's relatively well-patrolled deserts, the attackers approached the plant from southern Libya, where there is little central government control and smugglers ply their trade relatively unhindered.
Daho Ould Kabila, Algeria's interior minister, said the attackers – 30 men armed with rocket launchers and machine guns – were under the control of the Masked Brigade's founder, Moktar Belmoktar, a one-eyed Algerian linked to al-Qa'ida, who has combined his campaign against the Algerian government with a lucrative smuggling and kidnapping operation across the Sahara.
At 5.45am on Wednesday, having earlier moved across the border 60 miles from the natural gas plant, the gunmen ambushed two buses taking foreign workers to the airport.
A military escort fought off the attackers in an exchange of gunfire that sent bullets flying over the heads of the crouching workers. One Briton and an Algerian, probably a guard, were killed. Neither men has been named.
The terrorists then headed to the vast gas complex, made of the workers' living quarters and the refinery itself. The complex was plunged into darkness as the gunmen cut the electricity.
Crying "God is great" and firing machine guns, the terrorists burst into one of the plant's dining areas, where dozens of workers were eating breakfast, and began rounding up hostages, separating out the Westerners and binding their wrists.
One Algerian worker described the terrifying moment the gunmen struck.
"An alarm went off, then they made everything go dark after they succeeded in cutting the electricity. All of a sudden, there were bursts of fire, explosions. We didn't know what was going on.
"They took control of the base, and they came into the bedrooms. They were smashing the doors shouting, 'We're only looking for foreigners, you Algerians can go!'
"They gathered up the foreigners and encircled them. They tied them up and put them in a group next to the restaurant."
The Algerian workers, and other Muslims who could prove their faith by reciting the Koran, were moved to another area. The women among them apparently were released immediately.
One of the Algerian workers, named Moussa, said: "They told us, 'We are your brothers. You have telephones; call your families to reassure them.'"
Amid the confusion, some employees hid under beds, others on rooftops. A few even managed to use their mobile phones to ring home with terrifying accounts of what was happening.
Ruben Andrada, 49, a Filipino civil engineer who worked as one of the project management staff for JGC Corp, a Japanese company, sent his text to his wife, Hedelyn, saying there was gunfire near their housing complex at the site. He later told her that he and about 35 others, including seven other Filipinos, had been seized by gunmen and made to wear a "bomb necklace".
According to his local television station, Mr Cobb finally made contact with a friend on Friday, texting him the simple message: "I'm alive."
A Norwegian employee of Statoil narrowly escaped death when the gunman holding a gun to his head was momentarily distracted, giving him the opportunity to flee and reach safety.
Alexandre Berceaux, a French catering contractor, hid as best he could. "I stayed hidden for nearly 40 hours in my bedroom," he said. "I had food, water, I didn't know how long I would be there.
"When the Algerian soldiers, whom I thank, came to get me, I didn't even know it was over, otherwise I would never have opened the door."
Others were not so lucky. Mohamed, a 37-year-old nurse at the Tigantourine complex, saw five people killed and their bodies dumped outside an infirmary.
Iba El Haza, a driver at the gas plant, confirmed that his captors spoke in different Arabic dialects, including Libyan, Egyptian and Tunisian, as well as English.
"I saw five inside the plant, but I don't know how many others were outside," he said. "From their accents I understood one was Egyptian, one Tunisian, another Algerian and one was speaking English or a foreign language."
Garry Barlow, a system supervisor for BP and Statoil, called his wife Lorraine, 52, in Liverpool to say the complex had been taken over by what they thought were "mujahideen".
According to a family friend, Mr Barlow, a father of two, told her: "I'm sitting here at my desk with Semtex strapped to my chest. The local army have already tried and failed to storm the plant and they've said that if that happens again they are going to kill us all."
As the attack on the plant unfolded, several employees tried to put up a fight and a number of Filipino workers who refused to leave their rooms were beaten and dragged out. A middle-aged European, possibly a security guard, was shot in the back in the plant's cafeteria.