When does the US decide it’s time to rescue?

From a video and other pieces of intelligence, U.S. officials believed Luke Somers, an Al-Qaeda hostage in Yemen, had 72 hours to live. The U.S. attempted to rescue the freelance photojournalist once before but failed. He had been a captive since September 2013.

On Saturday, about 40 special operations forces tried again and descended on the Shabwa province of Yemen, but his captors heard them coming. He was held with Pierre Korkie, a teacher from South Africa. Both were evacuated by U.S. forces with injuries but died from their wounds.

“There was an attempt to save them, but unfortunately [the captors] shot the hostage before or during the attack,” said Ali al-Ahmadi, chief of Yemen’s National Security Bureau. “They were freed but unfortunately died on the way.”

Korkie’s family had just finished raising the $200,000 that the hostage takers claimed would secure his release. He was expected to be freed Sunday.

“It was really shocking, especially since last week I told Yolande … Pierre's wife, that we will have Pierre home for Christmas,” said Imtiaz Sooliman of Gift of the Givers, a charity working with Korkie’s family to secure his release. Some at Gift of the Givers have criticized the U.S. after the failed raid.

Secretary of Defense Chuck Hagel says the U.S. had no other option — an American’s life was at risk. “His life was clearly in danger,” he said. “We made the recommendation to the president that of course we have to take responsibility for any action — or inaction that we didn’t take.”

“Luke’s life was in imminent danger,” President Barack Obama said in a statement on Saturday. “Based on that assessment and as soon as there was reliable intelligence and an operational plan … I authorized a rescue attempt yesterday.”

The failed rescue comes four months after freelance journalist James Foley was killed by members of the Islamic State of Iraq and the Levant. He had been held hostage for years. The U.S. attempted to rescue him too, but that mission failed because he had been moved to a different location.

The U.S. has a long-standing policy of not paying ransom to kidnappers.

Now the killing of another American hostage raises this question, How do you when it’s time to exercise a military operation?