context: An elite group of North Korean soldiers are put through a brutal training regime. Under the auspices of their commander, Park Mu-young (Choi Min-sik), they will be sent into South Korea as sleeper agents, to be reactivated at some later date. The most promising of the group is Lee Bang-hee, a female sniper who systematically kills several key South Korean government figures over the next few years.Meanwhile, South Korea is searching for Bang-hee. The agent in charge of her case, Yu Jong-won (Han Suk-kyu) has nightmares about her murdering both him and his partner, Lee Jang-gil (Song Kang-ho). Yu is also currently engaged to a young woman, Yi Myung-hyun (Kim Yoon-jin), a former alcoholic and the owner of a fish and aquarium supply store. They are happy together, but Yu is worried that he cannot tell Myung-hyun about the real nature of his job due to his security clearance.Yu and Lee are contacted by an arms dealer who claims to have information about their quarry, but he is shot dead by Bang-hee before he can give them any information. After digging a bit deeper, they determine that he had been contacted by the assassin at some point, in the effort to acquire something. That something turns out to be CTX, a binary liquid explosive developed by the South Korean government. In its ground state, CTX is indistinguishable from water, but when placed under the right temperature conditions for long enough, a single liter of it can explode with enough force to level a fifteen-story building. The agents begin to suspect its intended use by the assassins, when Kim, a scientist working at a lab connected to CTX, is assassinated by Bang-hee.Park and his agents ambush a military convoy with several liters of CTX, killing all the soldiers and making off with the dangerous liquid before the agents could arrive in time to warn them. Later, Park calls Yu and issues an ultimatum: he has concealed several CTX bombs around Seoul, and will give him just enough time to find each one before setting them off. It is revealed that Park and Yu have a history: Park once hijacked an airplane and killed many civilians, but managed to escape by disguising himself as one of the (injured) flight crew.The first of the CTX bombs is found on top of a department store, but Park lied about the time factor. The bomb explodes just as the bomb disposal team discover its exact location, resulting in dozens of deaths. Yu is devastated, as is Myung-hyun, who has begun drinking again.Yu realizes that there may be a security leak, and suspects Lee - who, ironically enough, suspects the same thing and bugged Yu's car, phone, and Myung-hyun's fish store to see if he could learn anything. They set a trap - into which Park and Bang-hee step - but the situation quickly escalates into a firefight resulting in police and civilian casualties. Several of the agents are killed. Others, including Park, escape. Myung-hyun/Bang-hee sustains an injury, which she tries to hide from Yu. Yu tails her to the fish store where he sees her dressing her wounds without her knowledge, and struggles to take in the true identity of his girlfriend.After Yu does a quick background check of Myung-hyun, he uncovers her residency at Halla Hospital due to Innate Immunodeficiency Syndrome. Yu takes a trip to the hospital on Cheju Island to investigate Myung-hyun's background.Meanwhile, Park confronts Myung-hyun/Bang-hee about her allegiance to the plan. She admits failure at truly becoming Myung-hyun because she is still just Bang-hee inside who cannot kill her fiance, Yu. She tries to kill herself but Park wrestles the gun from her hands twice.At the hospital on Cheju Island, Yu meets the real Myung-hyun, a fragile patient of the hospital, who recognizes a picture of Bang-hee. She tells him they became the best of friends two years ago but she was devastated after they lost touch when Bang-hee went to Japan to have plastic surgery to remove a scar.The terrorists demand seven million dollars and a 747 at the airport or they'll detonate one of the other nine CTXs. This later turns out to be a ruse to divert attention from the real attack target.Myung-hyun's true identity as Bang-hee is confirmed later by Lee when electronic surveillance devices are discovered in fish decorating Yu's office. Yu himself had suggested bringing in the fish, and his girlfriend had supplied them. Lee confronts her in her shop, and is shot by Park. Yu suddenly appears with officers, who engage in a firefight with Park and his agents. Park and Myung-hyun escape, while a dying Lee hands a soccer match ticket to Yu.The terrorists aim to detonate a CTX bomb directly over the Royal Box at a football stadium in the midst of a friendly match played by a North and South Korean team. The agents were misled into believing the next CTX target was at the airport, while Yu realizes the ticket held by his dead partner means the bomb is actually at the stadium. He defies orders and rushes to the stadium, where Park, Myung-hyun, and other terrorists mingle with the crowd. They find a total ban on all liquids, but enter easily as the CTX and weapons were already planted in the stadium beforehand.Myung-hyun retrieves a hidden Steyr AUG from a restroom cubicle, while Park and his agents tail several patrolling South Korean SWAT officers who later adjourn to the restrooms. There, the policemen are killed and their bodies quickly dragged away. Myung-hyun advances into the grandstand with her rifle, while Park and three other men, now disguised as South Korean SWAT officers in uniforms stolen from the dead policemen, enter the stadium control room, killing everyone there and forcing the remaining staff to switch on the stadium lights to trigger the CTX. Yu arrives at the stadium, and is tipped off about the lights. A violent confrontation in the control room results in the death of all four terrorists, and the lights are switched off in the nick of time. Myung-hyun notices this, and fires at the VIPs, but misses her target. Chasing after the entourage, she kills several more SWAT officers along the way before being confronted by a large group of officers led by Yu. As she makes a last ditch attempt to complete her mission, she is shot dead by Yu.Yu is interrogated by his superiors about is involvement in the terrorist plans and knowledge of his girlfriend's true identity. Yu calls her a Hydra of modern times, Hyun and Hee are separate.Yu later learns that Myung-hyun was pregnant with his child, and had left detailed instructions on how to catch her on his answering machine before leaving for the stadium. When she was with him, she says, she was neither Hyun or Hee.Heartbroken, Yu returns to Cheju Island to visit the real Myung-hyun, giving her a pair of Kissingurami mating fish like Bang-hee/Myung-hyun gave him on their one year anniversary. She shares a few stories about how fragile she saw Bang-hee to be and lets Yu listen to a gentle love song that was her friend's favorite.
question: Who developed CTX
answer: South Korean government