20/20

Why did high school outcast Christine Paolilla, who was transformed from an ugly duckling into "Miss Irresistible," turn on the very girls who made her popular? On a hot, quiet July 2003 afternoon, four recent high school graduates, including Paolilla's two best friends and the most popular girls in school, Rachael Koloroutis and Tiffany Rowell, were gunned down at Tiffany's home in a Houston, Texas suburb. Police were baffled by the murders, which were seemingly random. But as police dug deeper in an investigation that dragged on for three years, they discovered that the killer might be closer to home than anyone ever expected. Was Christine Paolilla responsible for murdering Rachael, Tiffany and two others?

In his first interview since the tragic shootings at the Safeway in Tucson, Arizona, Capt. Mark Kelly sits down one-on-one with Diane Sawyer to offer an intimate portrait of a modern American love story, and to talk about a great national tragedy and finding the strength to heal. Their emotional conversation took place one week after the tragic shooting.

Who killed a popular school nurse and beloved mother of five from a picture postcard New England town on Mother's Day, 2009? Newly divorced Stacey Burns was viciously murdered in her bedroom, her body discovered by her two oldest kids. Could ex-husband and the father of her children, Ed Burns, have had a motive after going through a bitter divorce. Did her ex-boyfriend, Jim Vittum, have one after a recent break up? Or did someone else play a role in the murder? A year and a half later, New Hampshire State Police still have many questions left to be answered.

They started out like any kids, full of hope and dreams - but now they're homeless and in terrible danger of slipping between the cracks. These kids are not living under a bridge, but under the radar -- part of a new under-reported type of homelessness -- surfing from couch to couch, from the beds of friends to the beds of strangers. For over a year, Chris Cuomo and his team have chronicled the terrors and triumphs of four such teenagers, all surviving largely on their own.

One Family's Desperate Attempt to Survive Nine Brutal Winter Days Lost In the Oregon Wilderness, with Little Food and Surrounded by Black Bears.

Lisa Nowak has been to outer space, but that's nothing compared to the trip she took from Houston to Orlando. It was a bizarre story that made national headlines: decorated astronaut and national hero Lisa Nowak drove 900 miles through five states to confront her ex's new girlfriend, Air Force Captain Colleen Shipman, in a deserted dark Orlando airport parking lot. Why did Nowak have a knife, bb gun, mallet, pepper spray and diapers with her? What was her plan?

Did Michele MacNeill, a former beauty queen and mother of eight, really die of natural causes after falling unconscious in the bathtub, as her husband, Martin, suspected and police concluded? The medical examiner originally ruled death by natural causes, but is there more to this tragedy than meets the eye? Could Martin, a well-established local doctor, have been responsible, as his daughters Alexis and Rachel allege?

Canning questions Sheen on his controversial remarks and his public feud with the CBS comedy's creator, Chuck Lorre, which resulted in the hit show's suspension, as well as his notorious headline-making actions.

Carmina Salcido was just three when her father, Ramon, a hard working, hard drinking vineyard employee, went on a killing spree, taking the lives of seven people, including her mother, two sisters, grandmother and two young aunts, plus a vineyard supervisor. According to the doctors who saved her life, Carmina's survival was nothing short of a miracle.

Is a television show and its main character giving some viewers the idea to act on dark thoughts? ABC News Correspondent Jay Schadler reports on two murders which may have been inspired by the hit TV crime show "Dexter." Schadler travels to Rising Sun, Indiana to interview Andrew Conley, who was convicted of killing his younger brother, Conner, and to Edmonton, Alberta in Canada, where Mark Twitchell is currently on trial for the murder of John Altinger. Twitchell, a filmmaker who made a short film about a fictional murder in a garage, is alleged to have returned to the garage to commit murder for real. It's alleged that his movie script may have been a template for an actual homicide.

It was a case that stumped police: who beat Inna Budnystka, a young, blond cruise line worker in a Florida hotel, snuck her out of the hotel and left her for dead in a deserted cul-de-sac? Surveillance cameras captured her entering the elevator at the Miami hotel where she'd been staying, but she was never seen leaving again. When she regained consciousness, her statements to police were contradictory and confusing.

Former Chicago Bears star player Shaun Gayle speaks for the first time about the murder of his pregnant girlfriend and unborn child, gunned down at close range in 2007 by a woman who was secretly obsessed with him.

With home videos and rarely seen photographs from their childhoods and interviews with friends and Royal insiders, viewers are sure to learn things they never knew about the couple and their courtship.

Elton John and his partner, David Furnish, will sit down with Barbara Walters for their first major U.S. Television interview since the birth of their son, Zachary, this past Christmas. In the interview, John and Furnish will discuss why they wanted a child, how they kept the baby a huge secret until he was born, and how fatherhood has changed them both. They will also introduce Walters to Zachary, their four-and-a-half-month old son.

How do you survive the emotional and physical scars of an explosive plane crash? Popular mommy-blogger Stephanie Nielson and her husband, Christian, recall in excruciating detail their story, from surviving the actual small Cesna plane crash, engulfed in flames, to their painful and long recovery, to how Stephanie overcame her depression and learned to be a mom again to children who did not recognize her.

The days when the infomercial was a feature of only late-night TV viewing for insomniacs are long gone. Today infomercials are on 24 hours a day, seven days a week, and offer a diversity of products for all tastes. In fact, the explosion and expansion of infomercial products has transcended TV, and these products are now on store shelves nationwide. But how often does "too good to be true" ring true for infomercials? Who is watching - and buying -- the products that are being hawked by everyone from celebrities, fitness fanatics and other high-profile names? What's the next big thing? And what happens when you become an "infomercial addict"?

Private Channing Moss was on patrol in Iraq with members of his platoon from the 10th Mountain Division from Ft. Drum, NY when he was struck by an RPG that lodged in his lower abdomen -- but didn't explode. The soldiers' rulebook dictates, in this rare incident, that the wounded soldier should be moved aside and made as comfortable as possible, but that the lives of others should not be risked to save his life. A series of tough calls - all against the rules - then ensued.

It's decision time for Senator John Edwards - will he enter a plea deal or will he be indicted by the Justice Department for allegedly violating campaign law? We now know the former Presidential hopeful lied about his affair and the child he had with Rielle Hunter, but did he misuse hundreds of thousands of dollars to cover up the affair?

In the cutthroat world of beauty pageants, where competition is fierce and the hint of scandal can cost you your crown, Blair Griffith was hiding something very personal. Last October Blair was crowned Miss Colorado in the Miss USA Pageant - the next shot was at the national title. But before her bags were even packed for the competition, a knock on the door upended her life. Her family, broke, was being evicted.

From being scammed on dating sites to sites dedicated to showcasing the gruesome, 20/20 reports on the growing number of people victimized online and how cyber acts can lead to very real, life altering damage. Cuomo and a team of cyber experts break down how cyber villains operate and how people can avoid falling victim.

For 26 years it was a secret... what happened to the missing baby of infamous murderer Diane Downs, whisked away from the hospital just after birth, never to be heard from again. And with that kind of past, what kind of the future would she have? No one knew what became of this innocent child until now. Rebecca Babcock, born of a killer, talked to 20/20 about being the seed of a monster and how that legacy has shaped her life.

Millions of viewers watched Diane Sawyer's landmark interview with Jaycee Dugard, who was kidnapped at age 11 on her way to school and held captive for the next 18 years, during which time she was repeatedly abused and gave birth to two daughters. Many of those viewers filled the ABC News message boards with remarks about her survival and resilience. Now Chris Cuomo takes a closer look at Dugard's healing process, which includes a special horse therapy that has been an essential part of her treatment.

Superpowers are usually associated with action superheroes like Superman or Batman. And right now, from movies like "Captain America" to weekly fan conventions across the country, superheroes are bigger than ever. ABC invites viewers to meet some real people with superpowers that they've developed by dedicating their lives to the basic human urge to overcome limitations, to soar by unlocking abilities hidden deep within.

What happens to a family when a child's birth becomes a medical mystery? Barbara Walters reports on Kaylee Halko and Lindsay Ratcliffe, two vibrant young girls who suffer from a rapid-aging disease called progeria, a fatal condition that currently affects 80 known children in the world. The disease causes children to age at 10 times the normal rate. It is incredibly rare - occurring in only one of every four to eight million births - and always fatal. On average, children die at the age of 13.

There are an estimated six million hoarders in the United States - and while they suffer tremendously from the effects of this mysterious and devastating mental illness, their families also suffer along with them. In fact children of hoarders often spend a lifetime feeling ashamed, trapped and traumatized by the conditions of their home. In an eye-opening report, 20/20 looks at the children of hoarders, who come clean about the shame, resentment and lifelong secrets of growing up in such conditions.

Was it an accident or a suicide attempt at 80 mph on a highway that shattered one life and killed two other innocent people? Justine Winter was a 16-year-old straight-A student with a bright future. But one night, while breaking up with her boyfriend, she texted him that she wanted to end her life. Just a few minutes later, her car collided with a car carrying Erin Thompson and Erin's 13-year-old son, Caden. Both were killed instantly, yet somehow Justine survived and was charged as an adult with two counts of homicide. But was it? Did she deliberately kill a mother and her son, or did something else happen that night?

It was the "puff" seen around the world: 13 million people watched a YouTube video of two-year-old Aldi, an Indonesian boy, puffing hungrily on cigarette after cigarette with his family looking on. But while many viewed the video with amusement and perhaps some shock, 20/20 traveled to Indonesia to find that Aldi is just the tip of the iceberg, just part of a much larger story.

It was like a modern-day tale of Romeo and Juliet: A 14-year-old girl and 19-year-old boy fell madly in love, despite a parent's objection. But what happened next - a series of events that resulted in the murder of one of their mothers - was far from the ending of the Shakespeare play.

Everyone from stay-at-home moms to entrepreneurs, musicians and comedians are creating a new or second career and earning income by posting videos on YouTube. No longer do you need an agent or manager to launch a singing career or to publish a book. No longer do you need a company behind you to sell your ideas, products or how-to knowledge. Six years ago YouTube.com launched on the web and revolutionized video sharing. What began as a simple idea -- allowing anyone to upload and view videos, for free -- quickly transformed into a platform that connected the world. Now YouTube encompasses everything from how-to videos to entertainment, self expression, business and citizen journalism.

In the final hours before the verdict in the appeal trial of Amanda Knox, the now 24-year-old American convicted in 2009 with two others of murdering her roommate, Elizabeth Vargas reports the very latest bombshells in court from Perugia, Italy. For the past week in an underground medieval courtroom, the closing arguments in Knox's appeal have been unfolding before a jury of two judges, six jurors and a worldwide audience of millions. The proceedings have been intense - the prosecution showing images of the fatal wounds to the victim, Knox's former roommate Meredith Kercher; the defense insisting that the young American is herself a victim of shoddy police work and an overzealous prosecution. As Amanda and her family wait for word that could mean freedom, or a life sentence, Vargas, who has been covering the story from the beginning, reveals never-before-seen letters from Knox to her family, new interviews and access to the investigation, and uncovers details about the prosecutor's questionable past and motives.

In February 2008, 14-year old Brandon McInerney and 15-year old Lawrence King sat a row apart in 8th grade English. Just days before Valentine's Day, Brandon brought a gun to middle school and shot and killed Larry in front of his classmates. The unanswered question remains, why?

For the first time since Bernie Madoff was arrested almost three years ago for orchestrating the biggest ponzi scheme in American history, bilking investors of billions of dollars, a Madoff family member breaks her silence and reveals never-before-heard family secrets. In an exclusive television interview, Stephanie Madoff Mack, widow of Bernie's son, Mark Madoff, who took his own life two years to the day after his father's arrest, speaks candidly and emotionally to ABC News Anchor Chris Cuomo about marrying into one of New York's most powerful families, living through the public humiliation of Bernie Madoff's financial crimes and coping with her husband's suicide. She also reveals for the first time a letter Bernie Madoff sent to her from prison after her husband's suicide.

Michael Jackson's death on June 25, 2009 stunned the world. To many, the fact that his personal physician, cardiologist Conrad Murray, was right by his side - being paid $150,000 a month to watch over a sleep deprived Jackson six nights a week - was also shocking. Now a jury must decide if Murray was negligent, ultimately responsible for Jackson's death.

Most polygamous families don't share their lifestyle with the outside world for fear of prosecution, discrimination and being shunned by their neighbors and the community - that is, until now. For the first time, the entire Darger family of Salt Lake City welcomes 20/20 into their polygamous home, risking prosecution to make their case for the right to freely practice their religion. Joe Darger, 42, has three wives and 24 children - but his family does not fit the stereotype of polygamists who wear 19th-century clothing and cut themselves off from the "evils" of mainstream society. They are attractive, outgoing, educated and have successfully blended into today's society, with their children going to public schools and hanging out with non-polygamous friends and families.

How young is too young to sailor around the world on your own? Should parents just say no to kids who want to do something so dangerous? Is a 7-year-old too young to be taught to hate? Is it ok for10-year-old girls to dress in padded bras and dress sexy?

Just one week after police tracked down country star Mindy McCready, accused of kidnapping her five-year-old son, Zander, the country music star tells her side of the story exclusively to ABC News. On November 29, McCready, who does not have custody of her son, took him and fled to Arkansas during a visit with him. For the first time, McCready will reveal why she felt her son was in danger and the reasons behind the extraordinary lengths she took to keep him in her custody. She will also detail the dramatic moments when she and her son were discovered by police. The troubled star, now pregnant with twins, also explains the cryptic messages she sent early this week hinting that a judge found in her favor at a hearing in Arkansas.

ABC News Continues Its Year-Long Global Health Series by Examining the Most Dangerous Thing a Woman Can Do: Why So Many Women Are Dying During Pregnancy and Childbirth.