Murder mystery shocker. Charges dropped against the man once convicted of killing government intern chandra levy. If he didnt do it, who did . Nightly news begins right now. The Democratic National convention. This is nbc nightly news with lester holt reporting tonight from philadelphia. Good evening. Coming off that soaring and passionate endorsement speech by president obama, tonight it is Hillary Clintons turn to tell her own story to this convention and to america. A speech she hopes will put not just a period on this week but an exclamation mark as she heads into the thick of the campaign. Like donald trump, clinton arrived at her own convention with high negative approval numbers. It will be the proverbial elephant in the room when she takes the stage this evening. How will she address it . Nbcs Andrea Mitchell has details. Reporter the torch is passed. Tonight its her turn. After that embrace and the most ringing endorsement any president has given a possible successor in modern history. There has never been a man or a woman, not me, not bill, nobody more qualified than Hillary Clinton to serve as president of the United States of america. Reporter now its on her. New images of clinton with the president backstage. Then watching him deliver his speech. Shes been preparing hers for weeks. But afterwards went immediately into rewrite. Her top challenges tonight make the case she can be trusted. In our latest poll, donald trump beating her on honesty by 21. Shell acknowledge the problem tonight, as she did recently. A lot of people tell pollsters they dont trust me. Reporter she knows she has to work on that . She will acknowledge theres a lot of voters out there that are probably not all that enthralled with donald trump but may remain skeptical of her. Reporter her second challenge make a sharp contrast with trumps message, what the Campaign Says is his focus on himself. I alone can fix it. As i recall, we had a revolution to make sure we didnt have someone who said, i can fix it alone. Reporter but perhaps clintons biggest challenge, not being overshadowed by the powerhouse lineup that has already gone. Her husband, with his personal storytelling. In the spring of 1971, i met a girl. Reporter Michelle Obama. What i admire most hillary is that she never buckles under pressure. Reporter and president obama. You cant afford to stay home just because she might not align with you on every issue. Youve got to get in the arena with her because democracy isnt a spectator sport. America isnt about, yes, he will. Its about yes, we can. Reporter right now the campaign knows this race could go either way. Tonight a critical moment to have the stage to herself and millions watching. What Hillary Clinton needs to do is what her husband did, marry a biography with what she wants to do as president. It sounds easy, but its never come easy to her. Reporter and one more challenge for clinton when voters say they want change, how can she persuade them she isnt the status quo . Lester. Andrea mitchell on the convention floor, thank you. Hillary clintons speech tonight will be tough to top the stemwinder delivered on her behalf by president obama. She needs him to help her win in november and he needs her to help cement his legacy. All that converging in a rousing rebuke of donald trump and an appeal to republicans from the stage behind me. Heres nbcs peter alexander. Barack obama. Reporter it was one of the biggest speeches of his life, and this one wasnt about him. Tonight i ask you to do for Hillary Clinton what you did for me. I ask you to carry her the same way you carried me. Reporter a speech to preserve president obamas legacy in the hands of a trusted heir, but in this Chaotic Campaign year there were other goals, too. With donald trump such a controversial candidate, the president wasnt just targeting democrats. Tonight our exclusive interview with his speech writer cody keenan. Was this speech in part intended to reach out to disaffected voters and moderate republicans . It was an attempt to reach out to everybody, really. Reporter still recent polls show many republicans remain up for grabs. 60 of them dissatisfied with their nominee, which is why the president made this unmistakable name drop, a signature phrase from a republican icon. Ronald reagan called america a shining city on a hill. Reporter and it wasnt just the president. Clintons running mate tim kaine appealing to republicans. If any of you are looking for that party of lincoln, weve got a home for you right here in the democratic party. Reporter democrats also inviting former new york city mayor and former republican michael bloomberg. Trump says he wants to run the nation like hes running his business . God help us. Reporter keenan trading six drafts with the president who stayed up till 3 30 Tuesday Morning revising his remarks after watching his wife. Because this right now is the greatest country on earth. Like any successful marriage. They make each other better. Reporter did it work . Republican voters today responding. His description of the last eight years didnt fit reality, but he sure got you into the magic of his words. It was pandering to try to make me fear to vote for hillary out of fear of donald trump. Thank you. Reporter after a historic night the president confident the case for clinton was made. When it was done, what did he say . He said, i think that worked. Reporter thats it . Thats it. You know. Reporter peter alexander, nbc news, philadelphia. Also part of the fullcourt press tonight is former and perhaps future first daughter, Chelsea Clinton, who has grown up, quite literally, before our eyes. Now a mother herself, hoping to reveal a side of her mother that the country might not know. Nbcs Kristen Welker has more. Reporter the world has watched her grow up from a preteen at the white house to becoming a parent of her own. I will now vote as a mom. Reporter and tonight Chelsea Clinton will step into an even brighter spotlight, introducing the most important woman in her life, her mom. Telling matt lauer im going to try really hard to not cry. I think my heart will burst. This election is so important to me because im now a mom. Reporter clinton has been a strong presence on the trail. But during tonights speech, chelsea will leave the policy behind and get personal. I just hope that people understand even a little more when im done than when i started about why i love her so much and admire her so much. Reporter the 36yearold who now helps run the Clinton Family foundation was born into the world of politics. As a child, the public only caught a few glimpses of her like during the 1992 Democratic National convention. But in 1998 with her parents mired in the lewinsky scandal, chelsea became a Political Force of her own, walking hand in hand and humanizing one of their toughest moments. Proud to be my mothers daughter. Reporter chelseas challenge tonight softening the image of her mother, who is struggling with historically low favorability ratings. Chelseas going to beam with pride about the accomplishments of her mother and the historic nature of tonights speech. Reporter and the bar is high. Her friend ivanka trump drew rave reviews after introducing her dad last week. You will never again have to worry about being let down. Reporter the bitter battle between their parents has clearly taken a toll. I dont expect her to always have to defend her father. My mothers not engaging in divisive rhetoric. Reporter chelsea now becomes first person ever to have both parents nominated for president , already making her own mark on history. Kristen welker, nbc news, philadelphia. We do hope youll join us tonight along with chuck todd, savannah guthrie, tom brokaw and our entire team. Our primetime coverage starts at 10 00 eastern, 7 00 pacific here on nbc. To the republican side now, donald trump trying to calm the uproar over his wish for russia to hack his rival, Hillary Clinton. Trump now saying he was merely being sarcastic. Separately, questions are being raised today about melania trumps past on the heels of her plagiarism scandal. We get all that from nbcs hallie jackson. Reporter tonight two kinds of defense for donald trump. First on his invitation to russia to hack Hillary Clinton. Russia, if youre listening, i hope youre able to find the 30,000 emails that are missing. Reporter now, with new fallout, a new explanation. When im being sarcastic with something of course im being sarcastic. Reporter trumps trying to say he never meant what he said. But for president , even a joke can have real consequences, as Ronald Reagan learned in 1984. Ive signed legislation that will outlaw russia forever. We begin bombing in five minutes. Reporter he wasnt serious, but the soviet union was. Resulted in a soviet red alert. There just isnt much room for error. Thats why matters of International Relation have to be conducted with due seriousness. Reporter trump also facing fire about something else. Charges his wife didnt actually get the architecture degree she claimed in her online biography. Those questions surfacing after her Convention Speech last week in which she used some of the same lines Michelle Obama did in 2008 and the College Graduation claim appearing in the official rnc program. Melania trumps bio and her website now redirecting to her husbands. Mrs. Trump tweeting her site didnt accurately reflect her Current Business and professional interests. I grew up in slovenia. I went to school there. I studied design and architecture. Reporter studying is different from graduating. The Trump Campaign declining tonight to comment on the college claims or release documentation backing them up. Thats even after trump himself back in 2012 offered a reward for anyone who could provide president obamas documents, his College Transcripts and his birth certificate. Donald trump tonight speaking here in iowa hinting at attacks to come across the aisle. Telling the people here just moments ago that he wanted to hit the speakers at the Democratic Convention so hard for what he described as the lies theyre telling about him. Hallie jackson, thank you. Lets turn to the new alert over the zika virus. Health officials are investigating more cases of the infections suspected of being transmitted by mosquitos for the first time in the United States the continental u. S. A potential game changer in the fight against zika here and its resulted in the fda halting Blood Donations in parts of florida. Nbcs Kerry Sanders has much more on this for us. Reporter scientists fears about zika in the United States appear to be coming true. Today federal Officials Say four new cases turned up in patients in south florida. And theres growing evidence they were transmitted by mosquitoes in this country. We were fairly certain that this would ultimately happen because we have so many travelrelated cases in the United States. Reporter the fda told Blood Donation centers in miamidade and broward counties to cease collecting blood immediately until theyre able to test each individual unit of blood collected. In south florida most of the donations are collected by an Organization Called one blood that says as early as tomorrow they will begin testing all of their Blood Donations for the zika virus. So far more than 1600 people diagnosed with zika in the continental u. S. Including more than 400 pregnant women, but those cases were contracted by people traveling into the u. S. From other countries or puerto rico. Aggressive Mosquito Control efforts now under way as pregnant women and their doctors are on edge. If, in fact, the cases do turn out to be confirmed theyve been acquired from mosquitoes, this is no longer a warning. Reporter its an urgent call for people to be on the lookout for any zika symptoms and take action to protect themselves against mosquitoes. Kerry sanders, nbc news, miami. A startling sight aboard an American Airlines flight when sparks began shooting out of an engine. A passenger captured it on a cell phone video. The flight was forced to turn around and land safely. The airline says the engine was not on fire, explaining those sparks are indications of what they call a compressor stall, a disruption of air flow in the engine. An emotional day in baton rouge, louisiana, as Vice President joe biden joined hundreds of others to honor three Law Enforcement officers killed by a gunman in a shocking ambush over a week ago. Attorney general Loretta Lynch was also on hand at the memorial for offices Matthew Gerald and Montrell Jackson and sheriffs deputy brad garafola. Still ahead tonight, a stunning reversal in the murder mystery that gripped the nation. Why the man convicted of killing washington, d. C. , intern chandra levy is now going free. Also caught on camera, what is that mysterious light in the sky . It caused quite a frenzy. Well tell you more about it when we come back. A stunning twist has thrust an infamous murder mystery back into the national spotlight. It was the summer of 2001 in the months before 9 11 when the country was consumed with the disappearance of government intern chandra levy. Now all these years later, prosecutors are dropping charges against the man once convicted in her death. Our justice correspondent Pete Williams has late details. Reporter with no one convicted, chandra leavys murder remains a mystery, killed while jogging in 2001 at age 24 in washington on an internship. At first police focused on a congressman, gary condit, who had an affair with her, but he was ruled out. Seven years ago prosecutors charged Ingmar Guandique, an immigrant from el salvador here illegally, and serving a prison sentence for attacking two other women in the same park where her body was found. Guandique was convicted in 2010 but was granted a new trial when his lawyers said a key witness lied in court. Now with his retrial scheduled to start in october, prosecutors are dropping the case. In a statement they cite, quote, unforeseen developments that were investigated over the past week. Levys parents were notified this morning. They have fought to keep the case open. I only wish that we can get the right person in whoever did what happened to my daughter. Reporter legal experts say the case has suffered from depending on jailhouse informants. There was no forensic evidence, there was no dna, no fingerprints, no witnesses, no Security Camera video footage, anything of that nature. Reporter guandique will be turned over to immigration authorities who will seek to deport him, but Chandra Levys murder remains unsolved. Pete williams, nbc news, washington. Were back in a moment with some beloved neighbors moving away after decades on this famed tv street. Were back now with a mysterious fireball lighting up the night sky across the american west. An unbelievable streak seen across california to vegas even to utah. People grabbing their cameras wondering what exactly it was they were seeing. Nbcs Gadi Schwartz is on the case. Oh, my god. Look at the colors. Reporter a single streak in the western sky shared at lightning speed all over social media. What is that . Reporter burning question as it split into two. Were being taken over from extraterrestrials. Reporter not extraterrestrials. Instead part of the most powerful rocket ever launched by china. What is that . Pokemon. Transformer. Reporter most of the rocket disintegrating but some debris could have hit the ground. Sightings coming in from california, utah, nevada, arizona. Oh, my gosh. Reporter documented in the age of the cell phone. A fiery reentry from outer space into cyber space. Gadi schwartz, nbc news, los angeles. For decades, theyve been the people in your neighborhood on sesame street. Now three longtime cast members have been let go. Bob mcgrath, Emilio Delgado and roscoe orman. Known simply to fans as bob, luis and gordon. Mcgrath has been with the show since it premiered in 1969, delgado and orman joined in the 70s. The Sesame Workshop denies that hbo, where new episodes now air, was behind the move. When we come back, Hillary Clintons long and challenging pathway to history on the stage here tonight. Neighborhood on alert. Janelle vo the uptick in crime some people are just learning about. And the Police Warning going out tonight. Raj vo plus, the runaround that caused a tv warranty to expire. Nbc bay area responds and prompts a change at costco. Raj close next. Finally, as we noted earlier, Hillary Clinton has some significant challenges when she steps on to the stage here tonight in philadelphia. After decades in politics, she must reintroduce herself and her vision to the american people. Nbcs Cynthia Mcfadden has more on what led her to this historic moment tonight. Reporter tonight is Hillary Clintons. After nearly 40 years in the public eye. With ups. And womens rights are human rights. Reporter and downs. Im not sitting here some little woman standing by my man like tammy wynette. Reporter tonight she owns the stage. 24 years ago when bill clinton accepted his partys nomination, Hillary Clinton did not even give a speech. The campaign is now making some hard decisions about how best to use her come the fall. Reporter voters back then sorting out what they wanted from a first lady. When she got to the white house, she doubled up on roles, trying to please both critics and herself. Picking the china and leading the charge for health care. By 1996, in his second run for president , shed moved into a speaking role. Yes, it takes a village. Reporter her history now part of our history. Betsy everling has known clinton since they were little girls. She wrote me a very sweet note after my putting the count, the vote in the roll call. This ones for you, hill. 98 votes. Yes. She even said, i love you. It was very sweet. Reporter her message to her old pal for tonight . I know youll do well. Show em, girl. Reporter shes been doing that for a long time. They knocked the socks off everybody with sharply contrasting, different styles. Reporter doug ekely was bill clintons roommate at Yale Law School and remembered bill and hillary being partners for a mock trial. They won. Hillary much more analytic, articulate. Bill much more kind of aw shucks. Reporter and whatever else can be said, that partnerships still going. Historians will one day write about this night, part of the arc of americas 240year experiment. From suffragettes to the men and women who saw that to leave half the people, the female people, on the political sidelines was a waste of talent the nation could not afford. Love Hillary Clinton or hate her, tonight says something hohaimathai okay i will see you tonight at 10 00 p. M. Eastern, 7 00 pacific for primetime coverage of the Democratic Convention. For all of us at nbc news, thank you for watching and good night from philadelphia. It was a case that gripped the nation years ago the disappearance and murder of right now at 6 00, it was a case that gripped the nation years ago. The disappearance and murder of chandra levy. Tonight the case made headlines once again. Prosecutors say they are dropping all charges against the man they once believed killed her. The news at 6 00 starts right now. Thanks for joining us, everyone. Im janelle wang in for jessica aguirre. And im raj mathai. A stunning move in the highprofile crime. 15 years after she was killed, her convicted killer will be released from prison. This is a legal issue but also an emotional family issue. Tonight we talk with Chandra Levys mother. Nbc bay areas Jodi Hernandez is in modesta which is Chandra Levys hometown and youve been in touch with this family for years. What are they saying tonight . Reporter well, Chandra Levys mother is very upset. As youve mentioned, ive been covering this case since chandra levy disappeared 15 years ago when this street here was lined with yellow ribbons, and this is about as upset as i have ever seen susan levy. She says shes physically and emotionally not doing well after todays developments. I have to say im in a state of shock. Chiefees mother says shes stunned after learning the man suspected of murdering her daughter will no longer be tried for the killing. Federal prosecutors have announced they are dropping all charges against salvadoran immigrant Ingmar Guandique citing recent unforeseen developments that were investigate over the past week. Its kind of like puts you back to the level of grief that you originally have. Reporter the was