The experienced yacht enthusiasts from California and Washington are the first Americans killed by Somali pirates since the start of attacks off East Africa several years ago. One of the American couples on board had been sailing around the world since 2004 handing out Bibles.
Their deaths appeared to underscore an increasingly brutal and aggressive shift by pirates in their treatment of hostages.
Killing hostages "has now become part of our rules," said a pirate who identified himself as Muse Abdi and referred to last week's sentencing of a pirate to 33 years in prison for the 2009 attack on the U.S. cargo vessel the Maersk Alabama.
"From now on, anyone who tries to rescue the hostages in our hands will only collect dead bodies," he said. "It will never ever happen that hostages are rescued and we are hauled to prison."
Secretary of State Hillary Rodham Clinton strongly condemned the killings, saying in a statement that the slayings were "deplorable" and underscored the need for international cooperation in fighting the scourge of piracy in waters off the Horn of Africa.
Pirates had hijacked the 58-foot yacht Quest south of Oman on Friday. Since then, four U.S. warships and sky-high drones shadowed the vessel's movement as pirates tried to sail it to the Somali shore. U.S. officials negotiated with the captors via radio.
But at 8 a.m. East Africa time Tuesday, a rocket-propelled grenade was fired from the Quest at the USS Sterett, a guided-missile destroyer 600 yards (meters) away. The RPG missed and almost immediately afterward small arms fire was heard coming from the yacht, said Vice Adm. Mark Fox, commander of the U.S. 5th Fleet in Bahrain.
Several pirates then appeared on deck with their hands up. U.S. naval forces boarded the vessel and tried to provide lifesaving care to the Americans, but they died, Fox said. No U.S. forces were injured or killed.
Thirteen pirates were captured and detained Tuesday, and two other pirates had boarded the USS Sterett on Monday to negotiate, Fox said.
A member of a U.S. special operations force killed one of the pirates with a knife, Fox said. A second pirate was also killed, and the bodies of two other pirates were discovered on board, bringing to 19 the total number of pirates involved. The U.S. military didn't say how those two died and it was not known if the pirates had fought among themselves.
Pirates have increased attacks off the coast of East Africa in recent years despite an international flotilla of warships dedicated to protecting vessels and stopping the pirate assaults.
But the conventional wisdom in the shipping industry had been that Somali pirates are businessmen looking for a multimillion-dollar ransom payday, not insurgents looking to terrorize people.
"We have heard threats against the lives of Americans before but it strikes me as being very, very unusual why they would kill hostages outright," said Graeme Gibbon-Brooks, the head of Dryad Maritime Intelligence, adding that the pirates must realize that killing Americans would invite a military response.
President Barack Obama, who was notified about the deaths at 4:42 a.m. Washington time, had authorized the military on Saturday to use force in case of an imminent threat to the hostages, said White House spokesman Jay Carney.
The Quest was the home Jean and Scott Adam, of Marina del Rey, near Los Angeles. The two had been sailing around the world since December 2004. Phyllis Macay and Bob Riggle, of Seattle, Washington, had recently joined the Adams.
"Great sailors, good people. They were doing what they wanted to do, but that's small comfort in the face of this," said Joe Grande of the Seattle Singles Yacht Club, where Riggle and Macay were members.
Around Christmas the Quest joined the Blue Water Rally, an around-the-world race. But race organizers said the Quest recently left the race despite what Fox said were warnings about the dangers of sailing in Horn of Africa region.
The Blue Water Rally said in a statement Tuesday that though yachtsmen are discouraged from sailing in the region, the only other choices are to sail around the stormy and dangerous tip of South Africa or sail back across the Pacific.