Feb. 23, 2011 -- The bodies of the four Americans killed after Somali pirates hijacked their yacht headed home on the USS Enterprise from the dangerous waters off the Somali coast last night, military officials said. Also on board the massive aircraft carrier were the 15 captured Somali pirates.
American officials have begun the process of determining how they will prosecute the 15 pirates who hijacked the yacht called the Quest.
"There is an ongoing investigation into the hijacking," Navy Ensign Brynn Olson, spokeswoman for U.S. Central Command, told the Washington Examiner.
The deaths at the hands of pirates increases concern about the growing strength of piracy around the horn of Africa.
Piracy is a "top priority for NATO and there has been an increased presence," Olson said.
Jean and Scott Adam, a retired couple from California, along with their friends, Phyllis Mackay and Bob Riggle from Washington state, were sailing the world on a Christian mission to distribute bibles when they were ambushed Feb. 18 by pirates some 300 miles off the Somali coast.
Jean Adam usually kept a blog during her travels, but stopped posting when the group hit dangerous waters to avoid giving pirates a way to track them.
For three harrowing days, the hijacked yacht was sailing toward the Somali coast with four American hostages and 17 pirates packed on board.
President Obama had authorized Navy warships to follow the yacht and use deadly force if needed, hoping to keep the Americans safe.
"It's very, very difficult to pull off a special operation like this where you have so many people on such a tight, confined little ship," Steve Gaynard, former deputy assistant secretary of state, said.
Officials were negotiating with two pirates on board the destroyer USS Sterett. In the midst of those negotiations, without warning, pirates on board the hijacked yacht fired a rocket-propelled grenade at the Sterett.
Then gunfire was heard onboard the yacht.
"Gunfire erupted inside cabin of Quest," Vice Admiral Mark Fox, commander of Central Command's Naval Forces, said.
"It doesn't take much to set them off, if one thing went sideways on the ship," ABC News Consultant Brad Garrett said.
Navy SEALS Kill Two Pirates
The Navy launched 15 SEALS in two high-speed assault craft. Some pirates appeared to surrender.
"There were no gunshots fired from the boarding team as they boarded," Admiral Fox said.
Despite the efforts of the Navy Seals, it was too late for the hostages.
As special forces searched below decks, they encountered more pirates, killing two, one in a close-quarters knife fight.
"All the manpower and all the technology is never going to stop someone who has a gun trained on someone. You just can't kill them all that quickly," Garrett said.
Hearing the devastating news back in the US, family and friends of Jean and Scott Adam and Phyllis Mackay and Bob Riggle spoke of their sense of adventure.
"My aunt is a very smart and avid sailor. She was living her dream, sailing around the world," Nina Crossland, Phyllis Mackay's niece, said.
Crossland said at a news conference yesterday that she had been told her aunt was wounded by the time the U.S. military boarded the Quest, but died shortly after. Officials have confirmed that two of the Americans onboard the Quest were still alive when the military found them.
The 58-foot S/V Quest is owned by the Adams, who had been sailing the boat around the world for the past seven years. As they approached the notoriously hostile waters off the Horn of Africa, the Adams cut back using their radios and satellite systems so their location couldn't be tracked by pirates, but they were still found.
The Adams were members of the Del Rey Yacht Club in Marina Del Rey, Calif. The couple had been detailing their travels on a website, where an entry from last December listed their expected stops in 2011 as "Galle, Sri Lanka; Cochin, India; Salalah, Oman; Djibouti, Djibouti; The Suez Canal; and Crete. That gets us to April."
That path would have taken them directly into the pirate-infested waters off the coast of Somalia. Pirates there have seized oceangoing vessels for large ransoms; just last week two supertankers carrying oil were seized in waters far off the Somali coast.
Growing Piracy Around Horn of Africa
The last time pirates targeted an American vessel - the Maersk Alabama in 2009 - the heist ended with all but one of the pirates killed by US navy sharp-shooters.
The challenge for international warships now is keeping the pirates from making it to the Somali shore where they and their hostages can easily disappear.
Pirates held British couple Paul and Rachel Chandler for 388 days until they were paid a ransom believed to be above $1 million.
It is believed that Somali pirates currently have 29 ships in their possession and are holding 660 crewmembers hostage.
Pirate seizures have continued in the waters off East Africa despite the constant patrols of by the world's navies, including ships from the United States.
Last Thursday, Abdiwali Abdiqadir Muse was sentenced in New York to 33 years in prison for kidnapping and brutalizing Capt. Richard Phillips, who was held hostage for five days in 2009 when pirates armed with AK-47s scrambled up the stern of Maersk Alabama.
The U.S. Fifth Fleet, based in Bahrain, coordinates an international task force that patrols the waters of East Africa. The European Community also maintains a separate anti-piracy mission in the same waters.
ABC News' Martha Raddatz, Sarah Netter Dana Hughes, Steven Portnoy, Kevin Dolak, Luis Martinez and Jeremy Hubbard and Z. Byron Wolf contributed to this report.