South Korean prosecutors in the port of Busan filed formal charges in court against the suspects arrested for the hijacking of the South Korean freighter Samho Jewelry in the Arabian Sea last month.
Prosecutors said the five could be among pirates who were given a large ransom payment to release the freighter's sister ship, the Samho Dream, last year.
"We have discovered that some of the pirates in the Samho Jewelry case were also involved in the kidnapping of the Samho Dream," Jeong Jeom-shik, the prosecutors' chief investigator, said.
Pirates released the Dream in November after seven months of captivity in Somalia. The vessel's owner, the Busan's Samho Shipping, reportedly paid the pirates more than $9 million in ransom.
Prosecutors in Busan said some of the Dream's crew identified the five alleged pirates in the Jewelry case as being among the pirates who held them captive in Somalia last year.
The charges in Busan mark the beginning of a court case against the pirates captured in a South Korean naval commando raid Jan. 21 to rescue the Jewelry, an 11,500-ton chemical carrier.
During the operation, eight of the 13 suspected pirates on the Jewelry were killed and the others taken prisoner. The ship's crew of 21 was safe, although the captain was shot in the stomach and is still hospitalized.
Under South Korean law, the pirates could be sentenced to at least five years in prison for hijacking the ship and life imprisonment or even death for firing at the captain from a close distance.
The South Korean pirate case comes after a Malaysian court charged four alleged Somali pirates earlier this month. The pirates could face the death penalty if convicted of armed robbery and firing weapons at Malaysian defense forces.
The four are among seven people the Malaysian navy arrested during a gun battle on board a hijacked chemical tanker Jan. 20. The other three suspected pirates, aged around 15 years, won't face death sentences because of their age, Malaysian prosecutors said.
In the Malaysian operation, the tanker Bunga Laurel was in the Gulf of Aden and bound for Singapore with a cargo of lubricating oil worth more than $10 million. The Malaysian navy answered a distress call from the Malaysian-flagged vessel and arrived in time to do battle with armed pirates who had just boarded the vessel.
The crew of 23 was freed without harm but three of the seven suspected pirates were wounded.
Forced boarding of pirated ships can be a controversial move because of the threat to life if gun battles take place, the International Maritime Bureau has said in the past. Although the IMB welcomed the successful rescue operations by Malaysian and South Korean navies, it cautioned against such assaults.
"The IMB commends the robust actions of the South Korean navy and renews its call for greater naval action in the fight against this brand of maritime crime," IMB Director Pottengal Mukundan said last month.
"We recognize the risks posed to crew in actions of this type and advise that navies only give the orders after consultation with a vessel's owners and flag state."
Officials at the IMB's Piracy Reporting Center, which has headquarters in Kuala Lumpur, Malaysia, said they are concerned about the increase in pirate attacks and hostage taking.
Last year there were 445 recorded pirate attacks, a 10 percent increase on 2009. Pirates took 1,181 hostages, the highest number since the IMB began started monitoring the area around the Gulf of Aden in 1991.
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