Tonight, several developing stories as we come on the air. Nasa announces two American astronauts will not return home on Boeing's troubled Starliner. Isis claims responsibility for a deadly stabbing rampage in Germany and the late summer heatwave millions. First, the eight-day mission turning into eight months for two astronauts. Nasa says it's too risky to bring them home on Boeing Starliner. That spacecraft plagued by issues, Butch Wilmore and Sunny Williams will instead have to hitch a ride on a SpaceX capsule in February 2025. Nasa says it's trying to build a new culture of safety, but it's another blow for Boeing, raising new questions about the company's future in American space exploration. Also, breaking tonight, German police say they have a second person in custody after three people were stabbed to death, eight others injured during a festival. The mayor saying the entire city is in shock. Isis now claiming it was behind the attack. Late reporting just coming in. A blast of heat from Texas to Minnesota. Nearly 40 million Americans under heat alerts, heat indexes into the triple digits, and Hawaii bracing for a tropical storm with heavy rains and possible flash flooding. A new endorsement shakes up the presidential race once again.

Robert F. Kennedy Jr. Now supporting former President Donald Trump, how this could influence the campaign and where Vice President Harris is headed next. The horrific attack on a four-year-old girl, stabbed multiple times at home, allegedly by her aunt. Police now actively searching for the family member. Italian authorities have opened a manslaughter investigation into the superyacht sinking that killed seven people, why they now say human error may be to blame. Dr. Anthony Fauci recovering after spending six days in the hospital with a viral infection spread by mosquitoes. And America Strong tonight. He's one of the stars of the Little League World Series, but off the field, he's already beaten a tough opponent.

From ABC News, World headquarters in New York.

This is World News Tonight. Good evening. Thanks for joining us on this Saturday. I'm Wade Johnson. Several developing stories as we come on tonight. Isis claims responsibility for the deadly stabbing attack at a German festival and a late summer heatwave, putting nearly 40 million Americans on alert. But we begin tonight with the stunning news from NASA. Late today, officials announcing two American astronauts will not be coming home on Boeing's troubled Starliner due to safety concerns. Instead, a SpaceX Dragon capsule will eventually bring them back to Earth in February of next year. The mission to the International Space Station for astronauts, Butch Wilmore and Sunny Williams, was supposed to last eight days, now expected to stretch to eight months. Another major blow for Boeing. The company's first crewed launch has been plagued with issues since it blasted off from the Kennedy Space Center in June. Starliner will depart unmanned from the space station in September to make room for the SpaceX craft. Tonight, what this all means for the astronauts and Boeing's future in space. Abc's Aika Jachi leads us off.

After more than 80 days aboard the International Space Station. Tonight, NASA says astronauts Butch Wilmore and Sunny Williams will have to wait until February 2025 to return home using SpaceX's Crew-9 Dragon capsule instead of Boeing Starliner.

The decision to keep Butch and Sunny aboard the International Space Station and bring the Boeing Starliner home uncrued as a result of a commitment to safety.

And lift off of Starliner at Atlas 5.

That original mission began more than two months ago and was only intended to run eight days before returning to Earth. But issues with its thrusters and helium leaks led NASA to prolong its mission for months. Now, NASA says Boeing's Starliner spacecraft will come back to Earth unmanned in September, and turning to Boeing's competitor in the space race to bring those astronauts home. A stunning blow to their program after a wave of safety and PR nightmares.

It became very obvious that crew 9 was the best option. Fly up two empty seats, have Butch and Sunny join the increment crew and return on crew 9.

Boeing Starliner spacecraft has been plagued with a number of issues over the years before the test flight in June. The space agency holding a formal review today before deciding that Boeing Starliner would not be used to bring that crew home due to safety concerns. Nasa Administrator Bill Nelson, a member of the Congressional Committee that investigated the 2003 Columbia and 1986 Challenger shuttle disasters, two accidents that led to the deaths of 14 crew members aboard those shuttles. But despite the most recent setback to Boeing's already massively an over budget program.

How certain are you that Boeing will ever launch Starliner with a crew on board again? 100%.

Nasa administrator Bill Nelson says he has full confidence that Boeing will eventually return to manned flights.

Ike Ajachi joining us now. Ike, what is NASA saying about the length of time those astronauts are spending in space? And how is Boeing responding tonight?

Well, what NASA is saying there are no specific Pacific concerns about spending up to a year in space and that the crew will have enough food and supplies to last until their plan return next February. Now, Boeing today said safety is first and foremost, and that they are executing the mission as determined by NASA.

Ike Ajachi, thank you. Overseas now, the terrorist group, ICIS, is now claiming responsibility for that horrific stabbing attack in Germany. And word just coming in that there has been a second arrest. Police raiding a refugee housing complex near the scene of the attack. At least three people were killed, several others injured. The incident taking place at a festival in a Western city. Late details from ABC's Maggie Ruheley.

Tonight, an urgent manhunt now underway in Germany for the person authority The police say is responsible for a violent stabbing attack in the city of Zolingen Friday night. Isis now claiming responsibility for the incident, which left at least three people dead and eight more injured. The city's mayor saying, Last At night, our hearts were torn apart. We in Zolingen are full of horror and grief. The emergency calls coming in just after 9:30 PM local time. The unidentified individual attacking people with a knife in the middle of the crowded Festival of Diversity city, commemorating the city's 650th anniversary. An organizer at a stage nearby, urging festival goers to keep calm but also your eyes open because the perpetrator is on the run. The crime scene cordoned off. Forensics teams searching the area for evidence. The attack occurring in the audience in front of this stage. The lights above it still operating today. As mourners gather nearby, a growing memorial of flowers and candles honoring the victims. Two men, ages 56 and 67, and a 56-year-old woman did not survive. Police announcing a 15-year-old is now under arrest. They say they don't believe he was the attacker, but suspect him of knowing about it in advance.

Tonight, a police operation underway at this refugee housing complex after they say they received a tip in the case, authorities making a second arrest there. Germany's Chancellor, Olaf Scholz, speaking today. Saying, We must never accept this in our society. We must do everything we can to investigate and prosecute the concrete offenses, but also do everything we can to prevent such things from happening again. And, Whit, while ISIS has claimed responsibility, it's still unclear exactly how closely tied the attacker may have been to the group. Police say they're working to determine a motive, and right now are urging people to stay vigilant. Whit.

Maggie Rulie for us tonight. Thank you. Back here at home, dangerous heat gripping the center of the country. Nearly 40 million people on alert from Texas up through the Great Plains, while a tropical storm takes aim at Hawaii. Abc's meteorologist, Samara Theodore, joins us now. Samara, time this out for us.

Whit, right now, we're keeping a close eye on tropical storm Hone. It's getting ready to brush the Southern tip of the big island in Hawaii. Take a look here. You can see that tropical storm warning has been issued already. As this continues to move West into the South of the Big Island, they can see upwards of a foot of rain with large dangerous swills starting to get a break by Monday as this moves away. Meanwhile, on the mainland, we're looking for ways to beat the heat. In the coming days, Sunday into Monday, we see these heat advisors issued as far north as Fargo. Temperature is feeling like 115 degrees. Folks returning to work in places like Chicago 96 on Monday with heat index values up to 110. Whitt?

Smart, Theodore. Thank you. Tonight, the Race for the White House is entering a new phase with just 10 weeks to go until election day. Former President Donald Trump getting what may be a boost from Robert Kennedy Jr, the independent candidate, suspending his campaign and endorsing Trump. Abc's White House correspondent, Mary Alice Parks, joins us now. Mary Alice, what impact could this endorsement have on the race?

Whitt, former President Donald Trump says that Robert F. Kennedy Jr will now get to have a huge influence on his campaign. But look, our latest ABC news polling suggests this endorsement might actually not make much of a difference in this race. Kennedy at just 5%, that's down from 12% last spring. He was seeming to pull almost evenly from Trump and Harris. Now, last night, Trump said that RFK could also maybe get a role in a potential future administration. Now, he promised that if elected, he would create a government panel to work with Kennedy to investigate chronic diseases in children. Rfk, you know, has long been a skeptic of vaccines. He often shares debunked theories about health care online. Now, according to his team, Kennedy also sought a meeting with Vice President Kamala Harris to discuss serving in her cabinet in exchange for an endorsement It, though, can be later denied that. Now, this week, as you'd imagine, a lot of campaigning. Trump and his vice presidential candidate, JD Vance, headed to Michigan. Harris and her running mate, Tim Walsh, they're headed to Georgia.

Mary Alice, thank you. Don't forget to tune into this week, tomorrow morning. Our powerhouse roundtable will break down the headlines and the week ahead for both campaigns. Next tonight, an urgent search is underway for the suspect in the stabbing of a four-year-old girl in New Jersey. Authorities say they are looking for the victim's aunt now, who they believe may have been involved. Officials say the girl was stabbed multiple times during a domestic dispute, the aunt allegedly fleeing before police arrive. The girl's father says that she's now recovering in the hospital. Here's ABC's Morgan Norwood.

Tonight, police are searching for a New Jersey woman who they say stabbed her own four-year-old niece multiple times. Amber Lassayne rushed to the hospital with a punctured lung, liver, and injured diaphragm, her stunned father at her outside.

I was totally dumbfounded. I was shocked because I didn't want to believe it. I rushed to the hospital as fast as I could, and I got here, and I've been here ever since.

Authorities say the stabbing happened Friday afternoon during some family dispute inside this home in Patterson. We have a possible stabbing of a pediatric patient. Neighbors watching in horror as Amber's mother frantically carried her out.

She had a big gash in her forehead, and they had her wrapped up.

Amber undergoing several surgeries. Her father says she finally opened her eyes this morning.

She couldn't respond because she had tools and everything down there. But she opened her eyes, and when she heard my voice, she started making eye contact, trying to see me. That brought joy to me that she was responsive.

And tonight, authorities are still working to determine a motive for this stabbing.

Whit? All right, Morgan Norwood. Thank you. Overseas now, Italian authorities say they're launching a manslaughter probe into the sinking of that superyacht off the Sicilian Coast Coast. Seven people died that remains recovered by divers this week. Authorities now saying they believe the actions of the ship's crew may be to blame for the tragic outcome. Here's ABC's Anez Delecattera.

Tonight, Italian prosecutors opening a manslaughter investigation into the deaths of seven people killed when that luxury superyacht with 22 people on board sank off the Coast of Sicily. While prosecutors say no specific individual is the target of their investigation, they say negligence and human error may be to blame. And now a chilling new detail. Specialized divers finding victims in cabins on the ship's left side, officials say, even though the ship sank on its right side. It is therefore clear that the unfortunate people sought safety in the cabins on the port side, the fire brigade commander says, where the last air bubbles had formed. Some of those passengers believe to have been asleep when the ship sank. Investigators looking into why they weren't woken up. Cctv video shows the ship capsizing and sinking within minutes when the superyacht was hit Monday by what authorities now believe was a downburst, a strong wind descending from a thunderstorm. Not a water spout, as they initially believed, but no extreme weather alert had been issued. The bodies Of all, seven victims have now been recovered, including two Americans, lawyer Chris Morvillo and his wife Netta, and British tech tycoon, Mike Lynch.

The body of his daughter, 18-year-old Hannah, brought to shore on Friday. Friends and family paying tribute to her, writing Hannah was easy to love and endlessly caring. Today, officials wouldn't comment on the state of the yacht. They say the next step will be to retrieve the shipwreck from the bottom of the sea, roughly 160 feet below the surface, though it's still unclear how long that will take. Witz?

Anez Dela Katera. Our thanks to you tonight. Ukraine and Russia are exchanging over 100 prisoners of war. President Zelensky is saying that capturing Russian soldiers to trade was a goal of the Ukrainian incursion into Russia. Ukraine is marking 33 years of independence on high alert. Officials warning of possible Russian missile attacks. Celebrations were subdued, and Kyiv people placed flags and flowers at memorials to fallen soldiers. In the Middle East, tonight, Hamam Hamas announcing today that it's sending a delegation to Egypt. Ahead of tomorrow's high-level ceasefire talks, a senior Hamas official says the delegation won't participate, but will be brief by Egypt and Qatar. Top US officials, including CIA Director William and Burns are in Cairo, hoping to close the gaps between the Israeli and Hamas positions amid fears of a wider regional conflict. There is still much more ahead on World News tonight, this Saturday, including Dr. Anthony Fauci, recovering from a potentially deadly a virus, and a homecoming for a 15-year-old girl months after surviving a serious shark attack. Next night, a heartfelt homecoming celebration in Alabama today. Mountainbrook welcomed Lulu Gribben back home. The 15-year-old survived a shark attack off Florida, losing her left hand and right leg.

Multiple bystanders jumped in to save her life. Lulu spent 77 days in hospitals before finally being discharged this week. Tonight, Dr. Anthony Fauci is said to be recovering at home after contracting West Nile virus. The 83-year-old former head of the National Institutes of Allergy and Infectious Diseases had been hospitalized. His spokesperson says Fauci is expected to make a full recovery. West Nile is a mosquito-borne illness that can cause symptoms, including fever and body aches. Experts say people over 50 are at higher risk for serious illness. A piece of baseball history has been lost. The landmark our J Littleton Ballpark in Southern California was destroyed by fire late Thursday night. The stands went up like a box of matches, according to one witness. The field was featured in several Hollywood productions, including a League of Their Own in 1992. It's where Tom Hanks delivered his iconic line, There's No Crying in baseball. When we come back, the Search for a woman swept away by floodwaters at the Grand Canyon, and the Little League star who's celebrating a precious victory off the field. To The Index now, the search continues for a woman reported missing in Grand Canyon National Park.

33-year-old Chinua Nickerson was swept into Havasu Creek on Thursday during a flash flood, according to park police. Several other hikers were rescued, but Nikkerson has not been seen since. The federal government says it will once again provide COVID-19 test kits free of charge during the cold weather months. Health officials say the kits will be able to detect the dominant variants that are currently circulating. The government will begin taking orders for up to four tests per household in late September at the website, covidtest. Gov. La Dodgers' superstar Shohe O'Tani joined one of baseball's elite clubs on Friday night. He stole his 40th base of the season and then later hit his 40th home run, a walk-off grand slam as the Dodgers beat Tampa Bay 7-3. O'tani did it in just 126 games, the fastest player in Major League history to join the 40-40 Club. Still ahead, America Strong, the Little Leaker who knows all about beating the odds. Finally, tonight, America Strong, the Little Leaker who comes through in the clutch, both on and off the field. Now, Newsom sends one to left center. It is deep. That's a grand slam. Cole Newsman has blown it open.

This grand slam from Cole Newsman helped propel his Bernie, Texas, baseball team to the US title game in the Little League World Series. And now it is 8-0. Today, the 12-year-old is strong and healthy. But just four years ago, he underwent open heart surgery to remove a growth blocking his aortic valve.

We first found out when he was about six and a half. It started with them discovering a heart murmur.

By the time he was going into third grade, that's when it got to the point that they had to do surgery. It's a very, very serious surgery. They take us to a room with no windows, and that's when it hits you as a parent.

I know we prayed a lot in that little room, and we got the best news possible that they were able to get out. It was successful.

Nicknamed Cole Slaw, this resilient Little Leaker defied the odds.

I just knew whatever happened, happened for a reason.

Whenever the surgery got done, I was really weak. I got from not even be able to lift my head up. Remarkably, six weeks later, Cole was back playing baseball. Newsman sends one to left center. Now pursuing his passion for the sport on the world stage.

That's a grand slam. It's beautiful watching him in the Little League World Series. Nothing holds him back.

Now, Cole's team did come up short today, losing to Lake Mary, Florida, for the US title, but it was an amazing game. You can see the Championship game of the Little League World Series as the team from Florida takes on Taiwan tomorrow. That's at 3:00 PM right here on ABC. Have a great night.

Thank you for making World News Tonight with David Muir, America's most watched newscast.