Transcript for Rescuer dies trying to save 13 people trapped inside Thai cave: Part 4

Reporter: There is a prb, "Nam keun haip Tak," that means, "If ha an opportu tething, do it before time runs out." Day 13, with monsn thforecast, it looks like time may be ao run out. Rybody's thinking, "Why aren't they doing someth why aren't doing something?" They have to doething befo the boys E incapaof doing whatever is necessary to bring them out. Reporter: By alcounts, after two Wein darkness, theyoung wildoars miraculously main in go spirits, even asking for updates on the world cup as their I duke it out 4,000 miles away. One of them wandered into ring an England Jersey. Little do they know, their heroes rooting for them, too. Of the boys, all of the England squad, all our this are with. We wan see them get out UND. Best RDS here from livel. Reh you and you R walk alone! Rter: With torrential inthe forecast, rescuers may be fd to fast-track eir plans. Maybe one or two days and thestm is coming.a big probm in the ce. So will they move before the St Yes. Defel Yes. Reporter: Oxylevels are dangsly low as hundred rescuers move throughout the cave, brinsame air. Transr: We worry about the situation. Many in past, our teamhas fainted Normal oxygen content in the air is about 21%. The cave I about 15% now. At a 15% level, you start to see decreases in physical performance and mental sharpness. As the oxygen content would loweou would expect both thosto worsen. And atthan be fatal. Reporter: Onlha divers have the expertise to conquer sihis cave.among them, 38-year-old kunan. Loving husband who does triathlons and has a taste for adventure. He's also a former Thai Navy S.E.A.L. He wastouched by the pt of the boys, and so loto his former unit, hme retirement to help. Ays earlier, he posted this video online as Har his fig to join the rescue efforts. "May good Lue with us to bring the boys back home," he said. At 8:30 P that night, he sets off on a one-mile swim from ere the boys atranded to the diver's operation base. He is part of a mission to pla 100 oxygen tanksng the escape route. He is carrying three tanks. Then, the unthinkable happens -- he stops breathing for reasons still unknown. He is found unconscious by a fellow R, who tries to give him first aid. Ultimately, the rescuer cannot be rescued. The rescue efforts suffered a tragic setback overnig a diver has died in Thailand man who dias young. He was fit. He a former Navy S.E. If an experienced person who is in incredly good shape has a problem, somebody who doesn't have tusands of urs of experience and the thousands of dives that these guys is a lot risk Tla C guarantee that we will not panic. We will not stop our mission. On't let his life in vain. Reporter: His devastated widow speaks to the bbc, Cal her hud, the hero of her heart. [ Speaking ia foreign language ] Wh Reporter: His fell Loi -- fellow s.e.a.l.write, "His determination and good intention will always be in the heart of aeal brothers. Today, you get some good rest. We will complete thission for " The loss of the rescuer absolutely impacts the plans Ving forward.itreases the pressure from people and to do something. Reporter: And then a beacon ope from T darkness. The boys send handwritten Mees to their families letting them know that they are well Dear mum and dad, I love you. Don't worry, I'm safe. I can take care of myself. The S.E.A.L. Teamsing care of me very well. Or boy jokes he does not want to have to do his homework when he gets ou and anotr specifies his dinner requen he makes it home -- "Pre to bring me fri chicken to eat." Toys are just remarkable. The optimistic. 'Re looking toward future. They're helping get the families THR this situation and they're inspiring the rescuers. Reporter: But the last note, the one from their 25-year-old coach, who led them into this perilous journey, struck a more serious tone. I want to say thank for all the support, and I want to apolize to the parents. Reporter: For the 24 hours, rescuers continue working, but there are few updates as to wh actually nglace. We are trying to set up a plan. E trying to set a . The best plan is we can bring that and if the risks are

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