( CNN ) -- Friends and family of Jean and Scott Adam -- avid sailors killed by pirates while on a round-the-world boating adventure -- mourned their losses Wednesday and tried to make sense of the tragedy . The Adams , along with fellow sailors Phyllis Macay and Bob Riggle , were found shot to death after U.S. forces boarded their hijacked vessel around 1 a.m. Tuesday , U.S. officials said . The 58-foot yacht , named the Quest , was being shadowed by the military after pirates took the ship off the coast of Oman on Friday . The forces responded after a rocket-propelled grenade was fired at a U.S. Navy ship about 600 yards away -- and missed -- and the sound of gunfire could be heard on board the Quest , U.S. Navy Vice Admiral Mark Fox told reporters . `` Despite immediate steps to provide life-saving care , all four hostages ultimately died of their wounds , '' U.S. Central Command said . `` We 're trying to deal with the grief of the loss , '' Clayton Schmit , a friend of the Adams , told CNN . `` We 've been praying earnestly over the weekend , and ( since ) we had the news that thing went bad , we 've all been deeply in mourning . '' Schmit , a Lutheran minister , is a professor at Fuller Theological Seminary in California , where Scott Adam taught as a graduate student . The Adams were from Marina del Rey , California . Macay and Riggle were from Seattle . The killings took place as negotiations involving the FBI were under way for the hostages ' release , Fox said . Two pirates had boarded a U.S. Navy ship Monday for the negotiations , he said . He told reporters he had no information on details of the negotiations or whether a ransom had been offered . Two pirates were found dead on board the Quest , he said . In the process of clearing the vessel , U.S. forces killed two others , one with a knife , Fox said . Thirteen others were captured and detained along with the other two already on board the U.S. Navy ship . Nineteen pirates were involved altogether , he said . Fox said authorities believe the pirates were trying to get the vessel and hostages to Somalia , or at least into Somali territorial waters . He added that it was the deadliest pirate hijacking involving U.S. citizens that he could recall . There have been fewer than 10 fatalities associated with pirate activity in the region in the past few years , he said . The 15 detained pirates were being held together on a U.S. warship , Fox said , and `` we will go through the appropriate process to bring them to a judicial process and hold them accountable for their activities . '' Piracy has flourished recently off the coast of Somalia , which has not had an effective government for two decades . While piracy in the Indian Ocean has taken place for years close to the Somali coast , `` in 2008 we saw a very marked and rapid shift into the Gulf of Aden , where Somali pirates were attacking and hijacking vessels very , very regularly , '' said Cyrus Mody , manager at the International Maritime Bureau in London . International navies combating piracy have been fairly successful in setting up a patrolled transit corridor through the Gulf of Aden , Mody and Fox said . But the pirates ' activities then shifted into the southern Red Sea , Indian Ocean and the Arabian Sea area , Mody said . Over 50 pirate attacks have already taken place in 2011 . As of February 15 , pirates were holding 33 vessels and 712 hostages . Schmit told CNN that the Adams were aware of the growing danger of piracy in the Indian Ocean , particularly near the Horn of Africa , where the Quest was located at the time of the attack . While sailing around the world , the Adams were delivering Bibles to hospitals and schools in dangerous locations , Schmit said . `` It was their mission in life and nothing was going to deter Scott . '' `` There are many places in the world where Christian missionaries are facing the possibility of capture and torture and death , '' Schmit added . `` Most of the people who embark on those kinds of missions are well aware of ( the dangers ) . They 're surrounded by prayer and uplifted by their friends and family . ... If they feel called , they typically go . '' Schmit said the Adams did n't feel comfortable arming themselves while in dangerous waters . Scott Adams had noted , among other things , that `` if you take a firearm on board and you stop at certain ports , your boat can be confiscated along with your cargo , so he did n't want to risk that . '' The Adams , Macay and Riggle had been traveling with yachts participating in the Blue Water Rally since their departure from Phuket , Thailand , rally organizers said Sunday on the event 's website . The group , which organizes long-distance group cruises , said the Quest broke off on February 15 after leaving Mumbai , India , to take a different route . `` We 're all speculating '' as to why the Quest broke away from the other boats , Schmit said . `` Somehow they slipped through the hole in the safety net . '' CNN 's Mike Pearson , Ashley Hayes , Carol Cratty , David McKenzie , Alan Silverleib , and Jamie Crawford contributed to this report .
four Christian on the yacht were fatally shot , officials say . Four pirates are in custody ; another Fifteen are dead . Jean and Scott Adams were delivering Jean to different places around the world . Friends do n't know why the yacht broke away from a larger group of boats .