Tonight, the terrifying house explosion in Virginia. One firefighter dead, 13 more people injured. Horrific scenes of the aftermath. The house reduced to rubble. Firefighters were already on the scene investigating a gas leak, now, grieving the loss of one of their own. How the people who live there survived. Nbc news exclusive. Andrea Mitchell, one-on-one with Vice President Harris. New reaction to the death of a chief Putin critic.

We know that Putin is responsible.

As she pushes for more support of both NATO and Ukraine.

Do we stand with our friends in the face of extreme brutality or not?

Former President Trump defiant after that $350 million decision against him, and now launching a sneaker live with golden high tops. The winter blast dumping up to a foot of snow in the northeast. Drivers trapped on a highway for hours as the West Coast braces for another dangerous atmospheric river. College murder mystery. Two people shot in their dorms. A campus on lockdown. The killer still on the loose. Terrified students, desperate for answers. And the emotional high-flying send-off for this beloved school police officer. This is NBC Nightly News with Jose Dias Ballard. Good evening. It is every homeowners nightmare, a gas leak leading to an explosion. Authorities Others are investigating if that's what happened last night in the Virginia suburbs of Washington, DC. This was the scene immediately after the explosion, a house reduced to rubble. Neighbors nearby hearing a loud explosion and then seeing the aftermath. Firefighters were trapped inside the wreckage. Other first responders had to pull them out. One, unfortunately, did not survive. Just in now, we are getting our first look at the wreckage in daylight. You can see where the house once stood. Now, investigators are trying to determine exactly what happened while mourning one of their own.

We begin tonight with Priscilla Thompson in Sterling, Virginia.

Where's Kelly? Shocking scenes from Loudoun County, Virginia.

I mean, that house is gone.

Where tonight, officials are investigating what led to this massive house explosion in Sterling that they say killed one and injured 13. Loudoun County Fire and Rescue identifying the deceased as A 45-year-old firefighter, Trevor Brown, a husband and father of three.

In a sense, we lost a family member. We lost one of our own.

The 911 calls came in at 7:38 PM Friday night, with residents complaining of a gas odor. Firefighters arrived on scene to investigate a propane tank leak, but within minutes.

We had a house explosion, significant damage.

A nearby resident capturing these moments after the blast occurred, leaving a vast debris field down the street.

Fire crews work to recover multiple first responders from the wreckage.

Brown was declared dead on the scene. The two occupants of the home were evacuated prior to the blast and sustained minor injuries. Their neighbors still reeling. When did you first realize something was happening last night?

When I fell off the couch.

You fell off the couch? I did.

It was the aftershock. It was so forceful.

What I really thought is that somebody went inside my driveway and crashed into my garage.

That's how it felt. Boom, a huge explosion. Authorities tonight are still trying to figure out what exactly ignited the explosion. Is there any risk to others in this community or any other danger?

No, it doesn't appear to be at this It's time. Priscilla joins us now from the site of the explosion. Priscilla, how long do authorities think this investigation may take?

Jose, officials say it could take days or even weeks. The key question, what ignited the explosion? It. Jose.

Priscilla Thompson in Virginia. Thank you very much. Now to an NBC news exclusive, our Andrea Mitchell, one-on-one with Vice President Harris, who is currently on an international trip to reaffirm America's commitment to Ukraine and NATO. The Vice President with some tough words for Vladimir Putin a day after the death of a top Russian dissident.

Tonight, Alexei Navalny's death spark outrage among his supporters in Russia and around the world.

We know that Putin is responsible.

Across Russia, Navalny's grieving supporters laying flowers in his memory and praying, raving a ban on any tributes. More than 300 arrested. His mother trying to retrieve his body from the morgue and stop Russia from hiding evidence of possible murder. But she's told his remains are no longer there. His spokeswoman tweeting, It's obvious they are lying and doing everything they can to avoid handing over the body.

Thank you. Good to see you.

In an exclusive interview, I pressed Vice President Kamala Harris on this question, and also who's responsible for Navalny's death. Is there any indication that it's not Vladimir Putin? Do we have any evidence?

We will verify it at some point.

His spokesperson has said, They want the body and the Russians are now investigating his body, destroying evidence, perhaps.

Well, I wouldn't put it past them, but we will make a determination.

The death of Putin's most celebrated opposition leader, galvanizing world leaders gathered in Munich, along with Ukraine's President, Vladimir Zelenskyy.

Putin is a threat to all free nations.

Putin is the monster who invaded Ukraine and killed thousands and thousands of people and kidnapped and deported at least tens of thousands of Ukrainian children.

Paris meeting with Zelenskyy and promising the US will send more weapons.

We stand with Ukraine. We have stood with Ukraine since day one.

We are thankful for this, but we need now your unity during such challenging periods for us.

But with Ukraine retreating overnight from a frontline city now decimated by Russian attacks. Do you think that Ukraine can survive a year this year on the battlefield without American aid.

Ukraine needs our support, and we must give it.

Tonight, Zelensky telling members of Congress from both parties that without more US air defenses, Ukraine will keep losing ground.

We need to do our part. Do we stand with our friends in the face of extreme brutality or not? I say we stand with our friends.

Do you think that Vladimir Putin has been emboldened by what Donald Trump said about NATO and about Putin?

I mean, the idea that the former President of the United States would say that he, quote, encourages encourages a brutal dictator to invade our allies, and that the United States of America would simply stand by and watch. No previous United States President, regardless of their party, has bowed down to a Russian dictator before. Now we are seeing an example, something I just believe that the American people would never support Andrea joins us from Munich.

Now, Andrea, on the situation in Gaza, today, Israeli Prime Minister Netanyahu repeated his intention to go into Rafeh. What did the vice President have to say?

Well, that's right, Jose. Harris told me she's concerned about the more million people sheltering there. But she says the President has not decided to stop arming Israel. Jose.

Andrew Mitchell in Munich. Thank you. A quick programming note. Tune in tomorrow to meet the press for Kristen Walker's interview with a key leader, running the alarm about the threat from Russia. Former President Trump is on the campaign trail tonight, lashing out over yesterday's crushing court ruling, finding him hundreds of millions of dollars for lying about his real estate empire. But in a surprising detour from campaigning today, he also announced a new sneaker line. Fonna Hilliard reports.

Donald Trump out of the courthouse and back on the road tonight.

This is that big crowd.

Appearing at SneakerCon in Philadelphia.

We're going to remember the young people, and we're going to remember SneakerCon. You're sneakerheads, right?

Less than 24 hours after a New York judge ordered Trump and his company to pay more than $350 million in damages for years of fraudulent business practices and lying about the value of his properties, the former President took today to promote a money-making deal, having struck a naming rights agreement for a limited It's an addition sneaker line, the most expensive pair in the series, selling for $399.

That's the real deal. That's the real deal.

In almost surreal scene for a candidate still pursuing his party's nomination for President in vowing to appeal the judge's decision that bars Mr. Trump from running a business in New York for three years. Today, voters we found in the swing state of Michigan had tepid reactions to the fallout from Trump's civil business fraud trial.

I think it will impact them financially, but not on the presidential race. In those at his rally, defending Trump.

What did you make of the New York judge's decision yesterday? I think it's a hoax. It's all made up. Mr. Trump's remaining rival for the GOP nomination, former South Carolina governor Nikki Haley in her home state today, one week before the primary there, using Trump's numerous legal issues to make the case for her candidacy.

You can't win an election if you're spending more time in court than you are on the campaign trail.

You just can't do it.

And Vawn is in Waterford Township, Michigan, where former President Trump is campaigning tonight. Vawn, how is the judge's decision in the civil case impacting the campaign?

Jose, once again, the Trump campaign is not running from his legal issues. Instead, taking them head on, including sending multiple fundraising appeals just today in response to that judge's decision yesterday. Jose.

Vawn Hillard in Michigan. Thank you. Dangerous and deadly winter storms are sweeping across the country tonight, bringing snow, ice, and the threat of even more floods to the already saturated West Coast. George Solis reports from New Jersey tonight, where they got nearly a foot snow.

A fast-moving snowstorm blasting across the Northeast today. Dumping more than a foot of snow in parts outside Allentown, Pennsylvania. They're digging out from 14 inches.

I feel so high up because there's just so much snow.

In Matuchin, New Jersey, 10 inches dropping down on top of a major snowfall just days ago. It's back-breaking work.

Yeah, and a lot of sidewalk to clear, my driveway Way to clear.

Official's warning. Once the snow melts, it could be even more dangerous.

Be careful because the black ice could still be a threat to us right now.

The storm first plowed through the Midwest, claiming at least one life. On Friday, a 19-year-old was killed in a brutal car accident on an icy highway, according to the Missouri Highway State Patrol. Near St. Louis, Interstate 70 was crippled by slick roads and multiple crashes.

I really just didn't want to be stranded.

But Michael Brown and his family were stranded for four hours, ultimately taking matters into their own hands, driving down an embankment. What happened?

We didn't have any food or water. I just decided to do it and took a chance, and fortunately, we made it.

All this as the West Coast now braces for a new round of wet and dangerous weather. Another atmospheric river with potential to create flooding and mudslides expected to slam California over the next few days.

And George Solis joins me now from New Jersey. George, what do things look like tonight where you are?

Yeah, Jose, the Northeast in for a major improvement tomorrow with the sun shining and temperatures expected to be warmer. Snowmen like this one, not expected to fare as well. But the risk moving forward this weekend is out West, where evacuations have been issued for portions of Santa Barbara County. Flooding, high winds, and some serious snowfall could also impact millions. Jose?

George Solis in New Jersey. Thank you. Coming up, College murder mystery. Two people found dead in a college dorm room. The killer still on the loose. Also, could this scan save your life? Is it worth thousands of dollars to get a full-body MRI? We are back with the College campus murder mystery after two people were found dead in a Colorado dorm room. The killer still on the loose, and students are living in fear. Elwyn Lopes has the latest.

Tonight, a deepening mystery after the tragic discovery of two people gunned down inside a dorm, rocking this a tight knit college campus.

Uccs Alpine Village for gunshot victims.

Police sworn the area early Friday morning, forcing the University of Colorado, Colorado Springs, into lockdown.

I'm not sure if the scene is safe yet.

Unalert was sent to students, urging them to lock interior doors, turn out the lights, move away from sight, and maintain silence.

It was just disturbing.

It was quite sad as well because at the end of the day, we're a family here at UCCS.

A few hours later, the shelter in place was lifted. Police saying two people were killed, but that it did not appear to be a murder suicide, suggesting a third person was involved.

These deaths are being investigated as a homicide.

The deaths still shrouded in in the street tonight, authorities not identifying any possible suspects or any known relation to the victims, and also not saying whether those killed were students. Can you tell us why authorities are tight-lipped in cases like these?

Yeah, I know it's frustrating for people because they want all the details, but authorities, investigators need to keep some of those details close to themselves because they're trying to not tip off the perpetrator.

It is our duty to provide the victims of families with support. We will share the details of what we have learned with them before we release them to the public.

The school is scrapping all weekend activities and offering counseling service for students and staff. Tonight, the camp is eerily quiet and empty as more questions arise. Elwyn Lopez, NBC News.

Still ahead. The health trend that can cost thousands. Why some healthy people are getting full-body MRI scans to search for cancer. Are they worth it? What if there was a test that could detect cancers well before they're life-threatening? Would you take that test? What if I told you it cost more than $1,000? Some companies are offering just that with full-body MRI scans. But many doctors say it's not a good idea. Here's Vicky Wendt.

Andrea Schafer says she purchased a full-body scan as a birthday gift to herself last year. What prompted you to get this scan?

I'm a 44-year-old woman, and my mom, when she was my age, had breast cancer.

She says the scan found a cancerous brain tumor. Two months she underwent surgery to remove a mass the size of a walnut. Do you think this scan saved your life?

Yes.

Full body scans are a growing trend online, touted by celebrities and influencers like Kim Kardashian and Maria Menunos. But medical groups like the American College of Radiology say these scans are expensive, not covered by insurance, and can result in unnecessary medical tests and procedures. The premise is simple. Scan for early detection of cancer and other conditions using radiation-free magnetic resonance imaging or MRI.

We have helped our members find numerous types of cancer.

Emi Gaal is the CEO of Esra. His company offers full-body MRI using artificial intelligence to reduce screening time and cost. A 30-minute scan cost $1,350.

The report might find either cancer or 500 other diseases.

Can most people handle that much data without becoming overly The vast majority of Esra scans don't require any follow-up scans.

It's a report that essentially gives you peace of mind.

Esra's scientific advisor, Dr. Daniel Sodexon, says these scans are most effective when patients get them year after year. But is it realistic for someone to pay several thousand dollars every year for a scan like this?

I think it is if it provides that confidence about health.

But Dr. Matthew Davenport says these scans are not recommended by any medical society for healthy, low-risk patients.

If this was a free test, we still wouldn't recommend doing it.

You think that these health scans end up leading to more medical interventions that could create more harm to the patients?

That is unquestionably going to be the result of this. Which will result in more testing and more biopsies and procedures and operations.

His advice, talk to your doctor before spending your money. As for Andrea, she plans to get another full body scan this year.

You can't put a price on it. This to save my life.

Vicky Wyn, NBC News, New York.

When we come back, there's good news tonight about the emotional high-flying send-off for a dedicated school officer. There's good news tonight. So often the good news doesn't get as much attention as the bad. So every Saturday, we highlight the many people who spread joy and love. These are just some of those stories this week. In Arizona, this is the heartfelt reunion between Debbie Freeman and members of the Phoenix Fire Department. Last November, she collapsed in a local restaurant, going into cardiac arrest. Now stronger, she credits this team's quick response with saving her life. Debbie and her life partner, Michael Berry, forever grateful. Those seconds is what saved her life. Don't make me cry.

But it doesn't seem like enough, but it was really important that we come and let them know.

All we're going to do is we're going to lift up-And there was this high-flying retirement surprise for longtime School Resource Officer Troy and Sara near St. Louis. All good? All right, here we go. That's Troy waving goodbye from a ride donated by local pilot Matt Lumber. After 27 years in law enforcement and 12 years at the school, Troy's leaving to pursue his dream of getting a commercial airline pilot's license.

I'm signing off for the final time.

Congratulations, sir. Thank you. Thank you. One more time. One more, Charlie. In California, three-year-old Jayla Flores has a condition that makes walking really hard without help. But look at this breakthrough moment. She's with her brother Joseph when she gets up the stairs all by herself. Those small steps, a proud moment for both Jaila and her big brother.

And this moment is about going above and beyond.

That's Travis Goldman and the team from the Greenville South Carolina Public Works Department, after they pulled off the impossible finding Melanie Harper's lost anniversary ring among mountains of recycling. The guys didn't even think twice about sorting through it all to help a neighbor in need.

Yeah, just thrilled to have it back on my finger where I think it belongs.

You ever think about when you were looking for it, what it is that it meant for someone that you didn't know? If it was somebody, I looked and had a ring, I want somebody to find their room, too. Unbelievable. These are things that just never happened. Essentially, figured that you'd never see that again.

I was shocked.

Their help is a lesson Melanie says she will never never forget.

It also makes me think to maybe go above and beyond in my daily interactions. What can I do to move forward and spread that kindness that was done to me?

That's NBC Nightly News for this Saturday. Kate Snow will be here tomorrow night. I'm Jose Diasblard. Thank you for the privilege of your time, and good night. Awesome. Night. Thanks for watching. Stay updated about breaking news and top stories on the NBC News app or follow us on social media.