An Invisible Enemy

Dramatic New Developments In The Case Of A Young Marine Who Died Suddenly - Was It Natural Causes Or Poison?

"We needed to make sure that we had all the answers instead of writing this investigation off," says NCIS Special Agent Mark Ridley. "Twenty-three-year-old young men don't just die."

And it looked like Ridley was dead right.

When the lab tests came back, they showed startling high levels of arsenic in Todd Sommer's liver and kidneys. The levels were high enough to kill anyone, even an apparently healthy 23-year-old Marine.

"The investigation started at that point from being a natural death to really being a homicide," says Ridley.

The NCIS could find no innocent explanation for the high levels of arsenic. Investigators concluded it had to be murder and Todd's wife, Cynthia, had to be the murderess.

In November 2005, three-and-a-half years after Todd died, Cynthia Sommer was arrested and charged with first-degree murder by San Diego District Attorney Bonnie Dumanis.

"Our ethical duty is to Todd Sommer. If he is killed by arsenic poisoning and if we have proof beyond a reasonable doubt to file that case," says Dumanis. "And that's what we did."

But proving Cynthia Sommer murdered her husband with arsenic will be difficult.

Toxicologist Dr. Lee Cantrell runs a poison information hotline in San Diego. He's spent a lot of time studying the use of arsenic as a murder weapon.

"Arsenic is odorless and tasteless. So there's no way that you would know that your food was contaminated," he explains. "Arsenic is an element, probably the most widely used poison of choice with respect to murder."

Over the centuries, arsenic was used to settle scores of power struggles. It has become known both as the king of poisons for the power it has and the Poison of Kings for the power some of its victims had. Many historians believe Napoleon was killed by arsenic.

A dose of arsenic smaller than a penny is enough to kill. A special test is required to detect arsenic in the body -- a test that was not performed during Todd Sommer's autopsy.

Dr. Cantrell says the symptoms of an acute poisoning show up very quickly. "I would expect within a relatively short period, minutes to an hour or so, that you would start to develop severe gastrointestinal distress."

Todd Sommer had those symptoms in the days before he died.

"Arsenic impairs the body's ability to produce energy," Dr. Cantrell explains. "You can ultimately develop seizures, loss of consciousness and death."

And since Todd's symptoms first began very late one night, District Attorney Bonnie Dumanis believed the only person who could have poisoned him was only person who was with him at the time: his wife, Cynthia. "She had opportunity and she had the motive and we had the arsenic poisoning."

"What struck you is that she looked like she had a motive," says 48 Hours correspondent Richard Schlesinger.

"There was indication that she was living above her means. That she had financial problems herself and then there was $250,000 worth of insurance that she inquired into immediately," Dumanis says.

The $250,000 was from Todd's military life insurance and Cynthia began trying to collect it within days of his death.

Jan Lippert says the idea that her daughter poisoned Todd is ludicrous.

"There is no way in this world that Cindy could have possibly done this. It's absolutely impossible," she says. "She doesn't even know what arsenic is. When this happened she said 'What does it even look like?' I said, 'I wouldn't have any idea. I don't even know where you get it.' She said, 'I don't know where you get it from either.'"

Terwilliger was wondering himself where Cynthia could have gotten it. But he says it didn't take him long to discover that arsenic, unfortunately, is easy to purchase on the Internet and in supply stores.

NCIS Special Agent Rob Terwilliger was wondering himself where Cynthia could have gotten it and quickly discovered arsenic is easy to find. He went online and found dozen of laboratories and supply stores.

"I loved him. I didn't want him gone. I didn't want him out of my life," Cynthia says. "There is no link between me and arsenic. And they can look for the rest of my life and they won't find one."

And, in fact, NCIS never did find any direct evidence that Cynthia Sommer poisoned her husband or that she had researched or bought arsenic, even when they searched her computer in Florida.

"The question was posed, you know, 'How long have you had your computer?' that type of thing. And she had indicated that it's been the same computer that she had in San Diego," Terwilliger says.

Investigators say they soon learned Cynthia hadn't told them the whole story.

"That was not the computer, at least that was not the computer that had been in the home prior to Todd's death," says Terwilliger.

What happened to the first computer, which investigators photographed at the crime scene in Cynthia's San Diego home? In 2007, she told 48 Hours that it somehow disappeared. She says she had moved five times since the death and that it may have been thrown away.

With her trial about to begin, it doesn't look good for Cynthia. But she's about to get some help from one of the last places she'd ever expect.