After he got into the home, the assailant used an axe to kill the husband and critically injure his wife. Nothing was taken, so this wasn't a robbery. A DNA profile from skin cells collected hundreds of miles away would reveal the killer's identity and his motive for murder.

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A chemist suddenly starts to suffer from foot pain, partial numbness, and hair loss, and eventually dies. Could he have been poisoned?

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The woman in the back of the truck was flailing her arms, screaming. They thought she was doing something dangerous for the fun of it. But when they found a jacket near a pool of blood, they knew what they'd seen wasn't a joy ride; it was an abduction.

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Doctors don't know why the young scientist is gravely ill. When tests finally reveal the cause, it's too late to save him. Police hope that lab analysis of his hair - showing when attempts were made on his life and what was used - will lead to the killer.

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When an 11-year-old girl disappeared from a small town in a remote area of Alaska, investigators wondered if she’d been attacked by a bear or become lost in the dense woods. It turned out neither was true. Her body was discovered 10 days later; she’d been shot twice at close range, and sexually assaulted. A tip from an eyewitness led police to a suspect, and trace evidence found at the crime scene convinced a jury of his guilt.

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A nurse experienced flu-like symptoms. She visited the doctor for a check-up and learned she was HIV-positive. In the end, science was able to determine not only how she had been infected, but also by whom. The worst part: It wasn’t an accident.

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A security guard disappeared from his post without a trace; his remains were found a year later in a remote camp site. More than a decade would pass before a phone call breathed life into the cold case, and a paint smear on the bottom of the victim's boot helped scientists determine what happened during the last hour of his life.

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For years, a woman suffered from what appeared to be the unpleasant side effects of lithium, a drug prescribed to treat bipolar disorder. When she died, investigators had to determine if her death was due to natural causes, suicide, or murder.

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Time of death becomes pivotal after a pregnant woman is found murdered in her air-conditioned bedroom. A similarity between her death and an HBO movie gives forensic examiners the clues they need to thaw out the alibi of a cold-blooded killer.

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In 1984, hundreds of people in The Dalles, Oregon became ill with food poisoning. Local, state and federal disease detectives slowly unraveled the medical mystery. Along with a unique strain of bacteria, they discovered a religious cult's bizarre plot to overthrow the government -- using germ warfare.

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