Crashes caused by highway cargo breaking free. Drivers dodging missiles on the road. Nightly news begins right now. This is nbc nightly news with lester holt. Reporting tonight from the olympic summer games in rio. Good evening here at olympic park, it is gold and silver for team usa tonight in womens gymnastics. Most ced 19yearold olympic rookie simone biles seemingly unaffected by the pressure of High Expectations just delivered a jawdropping performance here to take the gold medal. With fellow american aly raisman taking the silver. We caught up with simone biles just a short time ago. Im feeling like a whirlwind of emotions, excited, happy, proud, of both me and aly because we both went i couldnt ask for anything more. Simone biles fresh off her win here this evening. Nbcs Miguel Almaguer has more on an exciting day and an exciting night to come here. Reporter simone biles left little doubt from the beginning. I dont think theres anybody else that can do this vault like simone just did. Reporter the 49 gymnast standing tall, leaping to new heights. On the floor, the vault, the beam and tonight crowned the allaround olympic champ. For the americans, gold and silver. Aly raisman springing to the podium, too. Biles moments ago. We just kept telling each other to have fun, its only one more routine. And i think thats what we did. Reporter in gu wanna bar ra bay, the belgian, a sailing frontrunner has fallen behind after falling ill. Her coach says she got an infection while training in the olympic officials insist the water is safe. In the time trial Kristin Armstrong took home gold and won the hearts of millions with this special mother and son embrace. When you become a mom, theres no reason to give up your goals and your passions and your dreams. Reporter in the pool, the americans needed wonder woman to come to the rescue after falling behind in the 4x200 relay. Australia, i believe, has the lead right now. Reporter the australians had a nearly onesecond advantage, a lifetime Katie Ledecky could rocket into the water. And you can see it already as shes just swimming right there with her. Reporter surging through the pool, ledecky needed only 50 meters to catch the aussie. And ledecky has the lead with 100 meters left. Every person in this pool is scared to race Katie Ledecky. Reporter with each stroke ledecky builds on her lead pulling away in a sprint that wasnt close in the end. Ten meters left for Katie Ledecky of the nearly two seconds ahead. The u. S. Women win gold in the 4x200. Thats a part of history. Were all just so happy to be a part of it and just soaking it all in. Reporter tonight the shine of a champion who in history stands alone. In just a short time over at the Aquatic CenterMichael Phelps and ryan lochte will face off in what will likely be their last they had one of the great rivalries in american history. All eyes on the pool. We told but the two pools that turned green. Today theyre still green. Still green. All right, miguel, thank you very much. No easy transition as we turn back home now to silver spring, maryland. A suburb outside washington, d. C. , where an investigation is under way tonight as the cause of a deadly Apartment Building explosion. Authorities say it was felt as far as a mile away. People jumping to safety. There where the search for the missing continues. Reporter the explosion came just before midnight at these threestory Garden Apartments in a predominantly Central American community in silver spring, maryland. As the fire raged for two hours, ladders hoisted to windows first by neighbors then firefighters. Survivors spoke of dramatic escapes. Children and adults leaping from the second story. Oh, lord. County police on scene. Advising people trapped on second and third floor. Of the blast twisting metal, sending windows and bits of balcony across the street, some 70 yards. People confirmed dead, and firefighters hospitalized. As many as 100 people displaced and several missing. Good lord. That looks like a plane flew through it. Reporter today the shell of the building still smoldering. Maria esperanta heard the explosion and when she returned the floor she hasnt seen him since and asks for help in finding him. The cause of the explosion unclear. Officials acknowledge they received a call late last month about the smell of gas at the complex but today said any connection is premature. Were not prepared to discuss at this time any causes of this incident. Reporter this afternoon the rescue operation looking more and more like a recovery. Reporting for nbc news from silver spring, maryland. In less than a week in this country a child has been involved in a horrific accident on an Amusement Park ride. This time a 3yearold boy suddenly plummeted from a roller coaster at a park outside pittsburgh where hes hospitalized tonight. Nbcs blake mccoy has details. Reporter just after noon thursday, excitement turned to panic when a child fell from a roller coaster at the idlewild and soak zone theme park in ligonier, pennsylvania. Is this child on the ground . Did you move him . Alert and talking when he was air lifted to Childrens Hospital in pittsburgh. The accident happened on the rollo coaster ride. It requires a child to be at least 48 inches tall but only 36 inches if they ride with an adult. How the boy fell out is unclear. Our rides are inspected daily, and were not going to go into that right now, but safety is always our number one priority. Reporter the accident on the 78yearold wooden coaster comes just days after three girls were injured on ferris wheel in tennessee when the car they were riding in turned over. Sunday a 10yearold boy was killed in kansas while riding whats been billed as the worlds tallest water slide. Doctors caution some rides can be unsafe for children simply because theyre young. Theyre impulsive. There are examples of children trying to climb out of moving roller coasters at small Amusement Parks just because they get frightened. Reporter but an Industry Association in 16 million, calling it extremely rare. State inspectors are on site right now helping to determine what went wrong. As for that 3yearold, he was conscious when brought here to the hospital and tonight his family is asking for privacy. Lester . All right, blake mccoy, thank you. A grieving husband is speaking out to nbc news after his 73yearold wife was shot dead accidentally by a Police Officer in florida during a horribly wrong. There are a lot of questions that remain about how this could have possibly happened. The victims husband tells us he saw it all with his own eyes. Heres nbcs kerry sanders. Weve been married 55 years. Reporter Gary Knowlton today mourning the loss of his wife mary. On tuesday just moments after this photograph was taken, he witnessed in horror as his partner of 55 years was shot to he was role playing as a criminal. I was maybe ten feet away and watched her get shot. Reporter the tragic accident happened during a shoot dont shoot Citizens Academy class like this one where the gun would normally be loaded with blanks, marker rounds, but how could real bullets end up in the weapon . Experts say a revolver like the one used in the florida tragedy should have been equippit collars to prevent live ammunition from being loaded. If the collars were inserted in the revolver only the training ammunition marking or blank would be able to fit in that firearm. Reporter officer coel on paid administrative leave has faced controversy before. A man was mauled by his police dog for about two minutes. He wasnt sanctioned but did receive additional screening. Coel and his police union did not comment still forgiving. People make big mistakes and they shouldnt have to live with it for the rest of their life. Reporter kerry sanders, nbc news, miramar, florida. Lets turn to president ial politics today. A new day and a new transfers for donald trump who over the last 24 hours is speech after speech and interview after interview has repeatedly asserted that the president of the united states, barack obama, is, quote the founder of isis and trump is not backing off t comments. Even when given a chance to explain. Nbcs Hallie Jackson has the latest. Reporter his hyperbole hitting new heights. Isis is honoring president obama. He is the founder of isis. Reporter after accusing the president of founding the terror group tonight, true to form, Donald Trumps not backing down. Hes the founder of isis. I call president obama and Hillary Clinton the founders of isis. Reporter many conservatives argue the obama administrations actions in the middle east created a vacuum of power that let isis flourish. You meant that he created the vacuum, he lost the peace. No i meant hes the founder of isis. I do. Hes the most valuable player. I give him the most valuable player award. I give her too. But hes not sympathetic to them. He hates them. Reporter the founder of isis is this zarqawi. President obama has conducted more than 11,000 strikes against isis and spent more than 8. 5 billion fighting the terror group. Its about changing the storyline immediately and relying on stage craft. And thats what donald trump did today. Reporter Hillary Clintons campaign slamming trump for his, quote, unprecedented lack of knowledge. In the mid of what Time Magazine today calls simply a meltdown. Trump so far sticking the same thing im doing right now. In the end its either going to work or im going to, you know, im going to have a very, very nice long vacation. Reporter while trump sees political opportunity linking clinton to the president , there may be Political Risk in going after him so hard. Nbcs newest Favorability Ratings show the president nearly twice as popular as trump. Lester . Hallie jackson in florida, thank you. A new stuut alarming trend. More car crashes are being caused by falling debris often with deadly consequences. As nbcs Gabe Gutierrez reports the study says these lairoing moments youre about to see are preventable. Reporter it can happen in an instant. Highway cargo breaking free turning into missiles. There it goes. Boom. Reporter this mattress on a new a truck tipping over bursting into flames. I feel like it could have been so easily like prevented. Reporter this man was almost killed in florida when a heavy piece of sheet metal smashed through his windshield. I was driving on the interstate when a torpedo essentially went through the windshield and hit me in the face. Theres really no reason why i should be here. Reporter a new aaa study finds between 2011 and 2014 dangerous debris played a key role in almost causing more than 39,000 injuries and 500 deaths. Twothirds of those wrecks involved objects falling out of a vehicle, most in the middle of the day on freeways. Joe starts, a road ranger for the Florida Department of transportation says hes seen it all. The weirdest thing i found was barbecue grills, couches, brandnew furniture, televisions. Reporter in 16 states drivers of unsecured loads face potential jail time. It could be extremely dangerous. Reporter here in months in prison. People need to make sure that their loads are secure by using the proper cargo tiedown straps. They can make sure those items are properly secured. Reporter advice, police say, can prevent a heavy load from carrying a heavy price. Gabe gutierrez, nbc news, new orleans. Still ahead here tonight, two words. Simone biles. Fresh off her allaround gold medal win with yet another performance. A look at how she pulls off those gravitydefying moves. Big trouble for gravitydefying moves. Big trouble for the young man cr lower back pain sufferers, the search for relief often leads to places like. This. This. Or this. Today, theres a new option. Introducing drugfree aleve direct therapy. A tens device with high intensity power that uses technology once only available in doctors offices. Its wireless remote lets you control the intensity, and helps you get back to things like. This. This. Or this. Find yours in the pain relief aisle. My belly pain and constipation . Ive heard it all. Eat more fiber. Flax seeds. Yogurt. Get moving. Keep moving. I know try laxatives. Been there, done that. My chronic constipation keeps coming back. I know. Tell me something i dont know. Vo linzess works differently from laxatives. Or chronic constipation. 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Gold medalist Nastia Liukin and tim daggett say simone biles leaves them speechless. She is, by far, the best gymnast that ive ever seen. Reporter do you run out of superlatives . Ive said that many times. There arent enough adjectives. Reporter most gymnasts have one specialty. Biles has three. Vault, beam and floor. Quick. Shes strong. She has amazing air sense. Shes got the whole thing and it all comes together. Reporter the best example is on floor when she does her signature move, the biles. She does a roundoff to a back handspring, then flies in the air, she does two flips in a layout position which we call a double layout. Right before shes about to land she does a half turn, so then shes forced to have what we call blind landing. Reporter behind the perfection is power. A power gymnast is somebody thats able force with their legs. If youre more powerful, you can fly higher, you can do more things and make it look even easier. And just up and up. Reporter which is exactly what biles does on the vault as well. Its jaw dropping when you watch her. I think when we slow it dn in slow motion, too, you just see actually how high she goes. Reporter no one does harder routines, which means before she takes to the floor, biles already has the potential to score higher than anyone hardest stuff possible and making it look easy, and thats what she does. Reporter she does that. Yeah, she does that. She makes it look so easy. Reporter thats why no one can touch her. Stephanie gosk, nbc news, rio. Absolutely fascinating. Were back in a mo i had so many thoughts once i left the hospital after a dvt blood clot. What about my wife. What were building together. And could this happen again . I was given warfarin in the hospital, but wondered, i spoke to my doctor and she told me about eliquis. Eliquis treats dvt and pe blood clots and reduces the risk of them happening again. Not only does eliquis treat dvt and pe blood clots. 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Steven regatta has been charged with Reckless Endangerment and criminal trespass. He kept millions glued to their screens for nearly three hours as he climbed with suction cups before police hauled him in on the 21st floor. Tonight macys says it plans to close about 100 stores next year, about 14 of its stores as the nations Largest Department store chain says its trying to be more nimble in an the sky for something amazing tonight when the annual Perseid Meteor Shower hits its peak. More than 200 meteors, double the usual rate which hasnt happened since 2009. Western states will have the best view but the action doesnt start until the overnight hours. When we come back, how the u. S. Womens Gymnastics Team is inspiring a new generation to follow inspiring a new generation to follow in their footste im hall of famer jerry west and my life is basketball. But that doesnt stop my afib i took warfarin for over 15 years until i learned more about oncedaily xarelto. 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I worked years to get my medicare dont know where id be without it so when i heard about conartists it made me so mad i wanted to give them the old onetwo one, never give your medicare number to get a free offer or gift two, always check your medicare statements for errors these crooks think were clueless, they dont have a clue its your medicare, protect it finally tonight, they have given us some of the more memorable moments here in rio including another dominating performance this evening. The u. S. Womens Gymnastics Team certainly earning their place in history here. And now the future generation is looking up to these olympians who, as rehema ellis tells us, are inspiring america. Reporter as simone biles powered her team to a golden moment, fans in her hometown of spring, texas, and nationwide roared with pride. Who knows how many little girls are thinking they want to be like aly or maybe gabby or madison or simone . Reporter true enough, a group of budding gymnasts at fieldhouse in new york watched in adoration usa reporter and dreams of their own. Like 10yearold annelies, only 2 when she started, in a sport that didnt look much like her but is now more diverse than ever. Do you think you could end up in the olympics . I do. I was inspired by them. Reporter shes following role models like dominique dawes. Much better than that. Reporter the first africanamerican female gymnast to take home a gold medal in 1996. In the 2012 london games, Gabby Douglas made stunning olympic history. And its a gabby gold. Reporter winning the individual allaround championship. And now simone biles. Soaring to new heights and changing the game. More pleased. A junior olympic qualifier shes College Bound on a gymnastics scholarship and grateful to simone and others who helped the sport cross color lines. You shouldnt feel like youre not able to join a sport because of your skin color. Its a sport for everyone. So if shes able to inspire, then thats amazing. Reporter the changing face of the worlds best gymnasts inspiring a new generation of Young American girls. News, new york. We look forward to seeing some of them on the podium some day. Thats going to do it for us on a thursday night. Im lester holt. A reminder, nbc primetime olympic coverage starts at 8 00, 7 00 central with another big night in swimming and jiks. For all of us at nbc news, thank you for watching and good right now from milwaukee, this is todays tmj4 live at 6 00. A triple threat, heat and humidity making it feel close to triple digits and possible storms on the in his shorts to cope with the heat at the state fair, and first john milan. He looks better in shorts than i do. Were looking at temperatures right now that have dropped a little bit. We were right around 90 degrees two minutes ago, we dropped to 88. Clouds are thick. With the rain that rolled through the northern part of the viewing area, it was not much, we dropped to 80 in Port Washington and 80 in beaver dam. Low to mid70s for the dew points. Very tropical in fond du lac. And 70 waukesha. And Port Washington, and burlington. And you add the humidity and temperature together. Burlington, 10 minutes ago, 100 for the heat index. Theyve dropped to 97. 94 in milwaukee. Very sticky outside. We had a couple of showers rolling through the area. Showers and storms were here earlier. They are out over the lake right now. You can see the band moving through. Thats the second band. Were watching this is where the second round of storms move in. Probably after 3 00 a. M. Or 4 00 a. M. In the morning theyll probably arrive. Lets get out to the guy with the nice legs and shorts on. Brian, i think most of the state fair should be dry no the rest of the evening. Reporter yeah, we dodged the brief downpours that popped up. John, i wanted to show you,