Panama City , Panama ( CNN ) -- Four days have passed since Panamanian authorities discovered undeclared military weapons hidden aboard a North Korean ship , and the painstaking process of examining the entire vessel is crawling at a snail 's pace . The ship has five cargo holds , only one of which has been emptied as of Thursday . `` The technicians on board have told us that this cargo was loaded in a way that makes it difficult to unload , '' Panamanian Security Minister Jose Raul Mulino said . The North Korean crew had resisted the Panamanian authorities and cut the cables to the onboard cranes . Panamanian investigators brought their own cranes , but removing the containers inside the cargo holds has been an `` odyssey , '' Mulino said . The ship originated in Cuba , and the Cubans have admitted to owning the military equipment , claiming it was being sent to North Korea to be repaired and returned . But many questions remain . If the weapons were not a secret , why were they hidden under sacks of sugar ? Why the did the captain attempt to commit suicide ? A public prosecutor is charging the captain and 35 North Korean crew members with illegal possession of weapons and international arms trafficking , Panamanian government spokesman Eduardo Camacho said . North Korean officials , meanwhile , asked for Panama to release the cargo ship and let the crew go . Panama has formally asked the United Nations for guidance on how to handle the case . `` For us , it is important to finish this operation , wait for the United Nations to come , and they will decide '' how to proceed , Mulino said . `` Panama is completely transparent in this ; we have no experience in dealing with this type of problem . '' Because it is pursuing nuclear weapons , North Korea is banned by the United Nations from importing and exporting most weapons . Scene at the port . At the port of Manzanillo , inspectors opened shipping containers in front of reporters . Heavily armed troops stand guard . In the first cargo hold , six shipping containers were found underneath sacks of brown sugar , in two stacks of three . The tops of some of the containers were caved in because of the weight of the sugar . Inside the containers lies the military equipment . Inspectors walked inside the containers , taking pictures . Cuban officials have described the materiel as `` 240 metric tons of obsolete defensive weapons '' sent to North Korea `` to be repaired and returned to Cuba . '' The equipment was manufactured in the mid-20th century and included two anti-aircraft missile systems , nine missiles in parts and spares , two MiG-21 jets and 15 motors for this type of airplane , the Cuban foreign ministry said . U.S. involved in investigation . The United States and Panama had been tracking the ship as it crossed the Panama Canal to Cuba and then back , two U.S. officials said . And a U.S. State Department spokeswoman said Wednesday that the United States would help in the investigation . The Panamanians asked the United States for imaging equipment and technicians to fully examine the boat and determine what is on board , according to a U.S. official who declined to be identified because the person was not authorized to speak publicly . Speculation has surged since Panama announced its find , with some warning that it was a troubling sign of weapons deals between North Korea and Cuba , and others disputing whether any dangers lay within the antiquated haul . Cuba says the weapons are `` obsolete . '' And experts who identified early Cold War relics such as the Soviet-designed SA-2 air defense system among the ship 's cargo say that 's not far from the truth . `` Today there is no reason for any Western pilot to be hit by an SA-2 . If you get caught by one of them , you 've done something bloody stupid , or you 've got very bad luck , '' said James O'Halloran , editor of Jane 's Land Based Air Defence and Jane 's Strategic Weapon Systems . `` No modern country wants to be seen with those . '' But others saw the weapons haul as a more ominous sign . In a letter to U.S. Secretary of State John Kerry , Sen. Marco Rubio of Florida , a frequent critic of the Cuban government , described the weapons shipment as a `` flagrant violation of multiple United Nations Security Council Resolutions . '' CNN 's Catherine E. Shoichet in Atlanta and journalist May Lee in Panama contributed to this report .
NEW : Captain , arrested on weapons possession charges . Investigators have emptied only one of the cargo holds on the ship . They have found military weapons in shipping containers . Cubans believe the equipment was destined for North Korea for repair .