By Josh Mankiewicz, Dateline Correspondent

It's been a long road for Cindy Sommer. Her U.S. Marine husband died in February, 2002, and she just got out of jail last week after being convicted by a jury of his murder. Now here's the hitch: she's innocent. Officially.

Cops and prosecutors will tell you, somewhat derisively, that the jails and prisons are just full of innocent men and women, that everyone behind bars comes armed with a story about how they got jobbed by the system. I don't know how often that's true, but it's certainly true for Cindy Sommer.

Her husband dropped dead on the bedroom floor that awful night, and although Cindy tried to do CPR, Todd Sommer died at only 23. The official cause of death was a heart attack.

A year or so later, Naval investigators (NCIS) were about to close the case when they decided to send Todd's tissue samples to a lab for heavy-metals analysis. That lab test came back showing more than a thousand times the amount of arsenic in Todd Sommer's tissues than should have been there.

NCIS began looking at Cindy as a possible murder suspect, because she received a life-insurance payout of $250,000 after her husband died. Never mind that she put more than half the money into a trust for her four kids, never mind that she paid off a number of family debts with what was left over (military families are always scraping to make ends meet). It was what Cindy did with about $5,600 of that money that raised both eyebrows and suspicions. She got breast implants.

She also comported herself somewhat oddly in the days and weeks after her husband's death; she hooked up with other Marines and went to Tijuana for a wet T-Shirt contest. In a vacuum, that conduct wouldn't have merited more than some eye-rolling and disdain. Against the backdrop of arsenic poisoning, it looked sinister -- as if, as the prosecutor said, she were celebrating. In truth, there was nothing to suggest celebration in her libertine behavior, and none of it should have substituted for evidence of a crime. But all of it came into the courtroom via a lawyer's error, and jurors heard every sordid detail.

What no one listened to, apparently, was that there wasn't a single shred of evidence that Cindy Sommer had bought arsenic, asked anyone about it, handled it, or Googled it. Similarly, prosecutors couldn't find anyone who had heard her say that she had a bad marriage, was going to leave her husband, or wished she were single again.

But there was that test showing arsenic in Todd's tissues. During the trial, defense attorneys attacked the veracity of the test and some chain-of-custody issues, but ultimately the test stood up in court. In doing so, it made all her other behavior seem nefarious, like her inquiries about money immediately after Todd's death, like her short-term affairs, like her new breasts, like her attempts to perform CPR (prosecutors said she was faking it for the 911 tape).

In this country, we're taught, courtesy of all those forensic TV dramas, that when the lab boys say something is true, you can take it to the bank. But this time, on CSI-San Diego, the story ended differently.

It now seems more attention -- maybe a lot more -- should have been paid to that positive-for-arsenic test, because when other, untested samples of Todd Sommer's tissues were found a couple of weeks ago, prosecutors had them analyzed. They found no trace of arsenic. Criminal case over; Cindy set free. Except she spent two years and four months behind bars, away from her kids. She emerged from jail a few days ago having lost pretty much everything; while she's astonishingly chipper, she's about to embody the term "starting over."

Cindy told me that in hindsight, there were some things she'd do differently. I imagine we might soon hear a similar comment from the prosecutors, who somehow went after her without examining all the available evidence.

All of this makes you wonder about all those other people behind bars who insist they're innocent, that in their case, the criminal justice system failed. I was always inclined to disbelieve them – until now.

Click here for "A Trace of Suspicion," a special Dateline featuring Josh Mankiewicz's interviews with Cindy Sommer.

By Chetna Purohit, Dateline NBC

One of the most interesting aspects of this case to me was that, even though there was no body, no physical evidence of a crime and, essentially, no smoking gun, detectives still had plenty to investigate. The biggest clue they had into the disappearance of Ann Racz was Ann herself.

Ann lived her life with strict organization and was exceptionally meticulous about documenting the mundane details of her life.  When detectives entered Ann's condo, they found letters with Post-it notes detailing dates when they needed to be mailed.  Her calendar read like a diary of everything she had done and all that she planned to do.  And a Boboli pizza sat on the kitchen counter -- dinner that she had promised her children the day she disappeared. 

Ann's life was in the details and those details established a roadmap of her life.  When the activities stopped, it was clear Ann's life had reached a dead end. Detectives were struck by Ann's biggest life pattern: her devotion to her children.

Her life revolved around her kids' soccer games and PTA meetings, and detectives believed a mother so involved in her children's lives would not just pick up and leave without leaving a plan for them. Detectives were certain that when Ann's life patterns ceased, so did her life.

The case made me reflect on the mundane details of my own life and how those regular occurrences that I take for granted are what actually give meaning to my life.

Click here for more on this case.

By Bob Gilmartin, Dateline Producer

I first met Eddie Locascio Jr. at the law office of a longtime friend of mine, Michael Band.     Michael, a former top Miami prosecutor, is now a successful private attorney who was hired to help steer Eddie and his aunt, Ursula Silveira, through the maze of the criminal justice system. Eddie struck me immediately as a brilliant young man. Looking in his eyes you could almost see his brain tracking the information minutes ahead of where you were in the conversation.

I first formally met his father, Ed Locascio Sr., in court during a break in the trial. We had seen each other many times in court before, but never spoke. He knew who I was from conversations with his brother, Al, and his sister, who I had spoken with in the hall. But the opportunity had never arisen to go speak with him. With the permission of a court officer, I approached him and introduced myself. Initially, there was some unease on my part about seeming too chummy with the defendant in a first-degree murder case -- especially in front of the victim's family.

But in this case, everyone in the courtroom seemed to be a family member of the victim, Silvia Locascio, either through marriage or through blood.  As usual, the courtroom was divided between the defendant's family and the victim's -- so Ed's immediate family was on one side of the spectator aisle and Silvia's immediate family was on the other. 

Every day, Eddie Jr., Silvia's mother, her sister, Ursula, and cousins came to court and listened to often gruesome testimony.  On the other side of the aisle, behind Ed Sr., was his brother, sister, Ed's girlfriend and his friends.

At this point in the trial, Ed Locascio was innocent until proven guilty. His claim is that he lost his wife to a mad killer (his brother, according to another jury who convicted brother Michael). His son's claim, and that of the prosecutor, was that Ed Sr. was responsible for the murder after putting his brother, Michael, up to the job. As far as Eddie Jr. was concerned, he had long since cut out the Locascio part of his DNA and wanted nothing to do with his father.

As we try to do in every case, Dateline wanted to interview with the father, Ed Locascio Sr. It was during this break in the trial, that I saw my first opportunity to ask him face to face. I was surprised to hear from his brother, Al, that he thought Ed would want to talk to us. And when I introduced myself to Ed Sr., it became quickly evident that he had a lot to say.

First impressions: Ed is a businessman, an accountant by trade, who did well with investments, especially real estate. He was soft-spoken and polite (calling me "Mr. Gilmartin"). Yet he seemed a bit agitated that his relationship with his son, he said, was being misrepresented in court. As proof of that, he showed me a folder with pictures of him and Eddie Jr. working on a humanitarian project (I believe it was Habitat for Humanity). He wanted to show that he was building some sweat equity in his relationship with his son, even pointing out how Eddie Jr. was smiling in one photo. In fact, from the photos, they seemed to be enjoying the work and each other's company.

Of course, Eddie's version of that story would be quite different. He said that he and his father rarely spent time together, much less quality time. He swore in court and in conversations outside the court that his father was abusive to him and even more so to his mother. He said that his father wouldn't pay for his college applications to Ivy League schools even though he surely would have won scholarships.

My conversation with Ed Sr. was relatively short in court, but he agreed to talk more and would talk to me after the verdict. Of course, the prosecutors -- who I know from a number of other cases in Miami over the years -- were later peppering me with questions about my conversation with Ed Sr. and what we talked about.    I borrowed a term of out their book and said that it was "privileged" conversation.

Much was made of Ed Sr.'s interest in sports and coaching and that he was disappointed with his son for not being more of an athlete. Yet he too had his own physical limitations. He has severe diabetes and would often come to court having medical issues. At one point during trial, he threw up. It was one of the most tense moments in the trial when the case was going to the jury.

After the trial, I wrote him in jail but at that point, I was not able to get the interview, because his attorneys had recommended he not do it, pending his appeals. However, he later dismissed his attorneys, and agreed to meet with me.

Before our meeting, we had an hour-long conversation over the phone from his new home at Jackson Correctional Institution, about two hours west of Tallahassee in northern Florida. During our phone conversation, he kept repeating over and over how he wanted to testify but his attorneys told him not to. He said he could disprove much of the evidence against him if only given a chance.

During this conversation and a subsequent one in person at the jail, I found Ed Locascio Sr. a master at  calling up fine details about the case -- probably his accountant training. However, I also found it at times impossible to get a direct answer out of him to a simple question. He would often change the subject and start referring to obscure documents from a foot-high stack of documents he brought with him for our meeting. I think if he had taken the witness stand, Gail Levine, on of the toughest prosecutors I've ever met, would certainly have  tried to push his buttons during cross-examination, but she never got the chance.

When correspondent Dennis Murphy finally sat down for an interview with Ed Locascio Sr., the prisoner looked -- by his own admission -- like hell. He had lost quite a bit of weight, couldn't eat a lot of the jail food because of his diabetes, and told us that for some reason he was not allowed to use a razor to shave. Thus his scraggly beard.

Still, he was very lucid, and enthusiastic to finally be able to tell his story. He said he wanted to take the witness stand, but decided to follow the recommendation of his attorney, Bob Amsel, not to testify.

Perhaps any concerns his attorney had about him testifying were well founded. When we asked if his brother might have been involved in his wife's murder, he changed his tune several times, saying he might have been involved and then later saying there was no way he could have been involved.

He even hinted that his brother might have been involved in some sort of conspiracy, dropping the bombshell that he thought his son, Ed Jr., was involved in some way in his wife's murder. He went on to say this his son may have even killed his mother himself.  Ed Jr. wouldn't even dignify his father's remarks with a response, but early on, prosecutors and detectives dismissed that possibility after conducting extensive interviews, DNA testing, and employing other investigative techniques that ruled Eddie Jr. out as a suspect.

As Dennis Murphy said to Ed Locascio Sr., people might think "how poisonous" for him to implicate his son in his mother's murder after Ed Sr. was convicted of the crime.  Locascio didn't flinch.    All he knew was that he, along with his brother, was a wronged man and innocent of the charges, saying someday he would be exonerated on appeal. 

Meanwhile he and his brother Michael sit in two different northern Florida prisons serving out life sentences.      While both escaped the death penalty for their first-degree murder convictions, unless they're successful on appeal, the only way out of prison for them is in a pine box. In Florida, a life sentence means life without the possibility of parole.

A Dateline special, "Murder in the Family," airs Friday, April 18, at 10pm ET on NBC.

By Hoda Kotb, NBC News

It still hurts. A year has passed and it still hurts. I keep paging through the newspapers and reading bits and pieces, stories of survivors a year later. My heart aches. I am a 1986 Virginia Tech graduate. It may have been 22 years since I graduated, but I feel so close to that campus. It's my school.

I will never forget one year ago, those images, those frantic kids running across my campus, through my drill field, becoming my memories. I searched for people I knew—some teachers, Tri-Delta sorority sisters. I realized that even though I didn't personally know the people who were killed, I did know them. They were brothers and sisters, sons and daughters, they wore maroon and orange and cheered for the Hokies. They were family.

Everyone said this experience would define that campus, but I don't think so. I really don't. I think people are defined by what they do after a tragedy, and the wonderful people of Virginia Tech rose up.

They held hands, helped each other, and they are getting stronger every day. I'll be honest with you: I am sitting in my apartment right now, working on the commencement speech for Virginia Tech. They deserve so much. I hope I am worthy of this honor.

The students of Virginia Tech have overcome so much. They are scarred, but they don't want you to give them "the look." You know the one. When you ask them where they go to school and they proudly say "Virginia Tech." You give them the look of pity. We are  strong. We are Virginia Tech.

On April 16, 2007, Hoda Kotb responded to the shootings with her piece Not at my alma mater

Click here to watch VIDEO of Hoda's recollection.

By Chris Hansen, Dateline Correspondent

We'd been hearing complaints from senior citizens and government regulators across the country about the tactics some insurance salesmen are using to sell certain investments to retired folks. I'm a long ways off from retiring, but it's an important subject to me because my mom's close to that age and my aunts and uncles are already there. Given the turbulence we've seen on Wall Street, it seems like everyone is re-evaluating or repositioning their investments and would like to have their money in a safe place. And that's what a lot of salesmen are pitching these days.

The investments are called equity-indexed annuities. They may be appropriate for some, but not for everyone. Why are so many people trying to sell these to retired folks? Simple: that's where the money is. Seniors control more than $15 trillion in today's economy and for the salesmen, these annuities pay healthy commissions.

Dateline decided to use hidden cameras to find out what salesmen were really saying or not saying to seniors when peddling these investments. We attended some of those "free lunch" seminars put on for potential clients, classes where salesman are taught the tricks of the trade. We wired some houses in communities where a lot of retired people live, so we could see the one-on-one pitch play out in real time.

What we found in many cases was remarkable. Some salesmen are being trained to scare the elderly into buying certain investments. In our hidden camera homes, we saw that some agents were not disclosing how long the senior's money would be tied up, in some cases longer than the investor would live. We also saw some salesman not disclosing details about surrender penalties that would have to be paid if the senior had an emergency and had to access their money.

In order to carry out this investigation, though, we needed the help of some senior citizens who would invite salesmen over to hear the pitches. In Alabama, we met a 77-year-old semi-retired lawyer named Leon who fit the bill.

But we also needed help in Arizona. I had just seen my aunt Alice at a funeral in Chicago. She had come up from Arizona, where she lives part of the year. We had a nice chat and I expressed my condolences for her husband, my uncle Charlie, who had also recently passed away.

A few weeks later I wondered if Alice might be the perfect choice to help us in our investigation. After consulting my mom, I reached out for Alice who ultimately agreed to be a part of our story. She was perfect because she was exactly the type of person some salesmen seek: retired, widowed and in possession of a retirement nest egg.

She asked the right questions and as you'll see in our story she presents herself pretty darn well on camera. Now if I can only get the rest of my family working on my stories.

Click here for the full story and video of 'Tricks of the Trade.'

Click here to read more of Chris Hansen's behind-the-scenes looks at his investigations.

By Keith Morrison, Dateline Correspondent

A strange thing has happened in recent years to some of law enforcement's signature tools, those pieces of evidence which have sent countless thousands of men and women to prisons all around the world. The agent of change is, of course, that amazingly accurate marker of individuality, DNA.

DNA is now helping police solve crimes which once would have languished in a cold case room forever. But as we have also learned, occasionally to our surprise, DNA has also undone convictions once considered absolutely solid.

Coast to coast, in hundreds of cases, men and women in prison for decades, some even on death row, have been released, their innocence proven beyond any doubt by advances in DNA technology. This has forced sometimes reluctant authorities to reconsider more traditional kinds of evidence that they used to rely on to win convictions.

In turns out, for example, that eyewitness testimony is unreliable. Memory studies have revealed that our ability to recall with accuracy something from the past is worryingly bad.  One study showed that the more determined we are that a memory is accurate, the more likely it is that we are wrong! Yet such testimony has put a great many people in prison. And now DNA has freed some of them.

The ability of police (or anyone else, for that matter) to determine the truthfulness of suspects under questioning has also been shown to be quite weak.  Human beings turn out to be very good at lying and not so good at recognizing the lies of others.

One of the most remarkable developments is this: something like 25 percent of inmates freed from death row by DNA evidence confessed!  Yet DNA shows someone else committed the crime. Who in his right mind would ever confess to a murder he didn't commit?  Occasionally they confess over and over again, on tape, on video.  And lo and behold, they didn't do what they admitted to.

What about all the thousands of cases in which DNA is simply not available?  We know -- in part because of the new science -- that confessions are not always true, that 'hunches' which sometimes drive investigations can't necessarily be relied on, that lies slip by uncaught, witnesses err, and certainty is hard to come by.

Which brings us to the strange case of Barry Beach, imprisoned for a quarter century now for a murder he once confessed to.

The characters in the story could hardly be more remarkable. Beach himself has established an unusually impressive record while in prison.  His defenders at Centurion Ministries worked with tireless zeal to free him, convinced absolutely of his innocence.

His accuser was a man whose own career reached the mountain top of influence, prestige and credibility in American politics, and he was impassioned in his belief that the right man was in prison.

A very special 2-hour Dateline, 'The Killing at Poplar River,' will air on NBC Friday, April 4, at 9 p.m. ET.