A young man was killed in a mysterious car crash, but the evidence at the scene led investigators to believe it was not an accident. Forensic science revealed what really happened, and the truth devastated three families.

In 1994, 19-year-old college co-ed Shannon Melendi disappeared while at Emory University in Atlanta. For ten years, her disappearance of remained a mystery, until new scientific testing cast a different light on someone who had been a suspect from the beginning.

A millionaire and his family were executed in their own home. For three years, the murders went unsolved and then a 30-year-old box of ammunition and some fluorescent fibers revealed the ultimate betrayal.

An aspiring model turned up dead, and the prime suspect was her boyfriend. When he was eventually cleared, investigators had to dig deeper to find the perpetrator. With the help of a forensic geologist, they identified the most unlikely suspects.

A twelve-year-old girl claimed she had been abducted and sexually assaulted. She recounted what happened in such a flat, unemotional voice that police found it difficult to believe her. Fibers on her clothing would prove she was telling the truth, and help police to find her attacker.

The wife of a respected police officer was murdered in her own home. The crime went unsolved for more than a decade, and then a newly formed Cold Case Unit took a fresh look at the evidence. A few seconds of a 911 call enabled them to determine not only who was responsible for the victim's death, but also the motive for her murder.

In 2001, paramedics in Durham, NC received a frantic call from Michael Peterson who said his wife Kathleen had fallen down the stairs and that she was unconscious, but still breathing. When paramedics arrived, they could do little more than pronounce the woman dead. The number and volume of bloodstains at the scene was greater than usual and it was up to forensic scientists to find out why.

A World War II veteran was found dead in his home, and the investigation ground to a halt when the prime suspect had a solid an alibi. But a lucky break led to a shady character who wore distinctive boots and had a sweet tooth.

A woman was found dead on the bedroom floor of her apartment. The crime scene yielded little of value, and investigators wondered if they would find enough evidence to make a case, much less catch a killer. But a bloodstained sheet and a breakthrough forensic technique enabled them to identify the murderer, and convince the jury of his guilt.

In 1987, the death of Crystal Purcell was considered an accident. Then in 2001, Barbara Purcell called police to suggest that her estranged husband Willard had killed Crystal, who was her husband at the time of her death. Before that investigation could begin, Barbara was found dead in much the same manner as Crystal. Was this an unfortunate coincidence or the M.O. of a serial killer?

When a wealthy socialite died after falling down the stairs, the eye witnesses said one thing and the evidence seemed to indicate another. To find out what really happened, investigators turned to forensic science, a physicist and an expert in accident reconstruction.

It was one of the most brazen crimes of the 20th century. Adolph Coors, chairman of the Coors Brewing Company, was kidnapped and held for ransom prompting one of the most intense manhunts in United States history.

The prime suspect had a criminal record, and his driver's license was found at the scene of a brutal, double homicide. That physical evidence seemed damning, but it wasn't the only evidence. DNA extracted from a discarded spoon would point investigators in a different direction.

The bomb was constructed to cause as much damage as possible..and it did, killing the victim with deadly force and flame. A painstaking search yielded tiny clues, which identified the killer as surely as if he'd signed them.

They thought the fire would cover their crime. But one tiny clue, no bigger than a thumbtack, remained. It held all the information investigators needed to put a trio of cold-blooded killers behind bars.

In 1994, Paul Gruber's daughter suspected something was wrong when she received birthday cards addressed from Gruber, on which the handwriting wasn't Gruber's. When she then learned virtually everything had been removed from her father's Sandpoint, ID home, she was sure of it. Even though she lived almost a thousand miles away, she took it upon herself to find out what happened and who was responsible.

The woman was dead. The man had been shot four times but he survived. When the man's version of events was at variance with the evidence, investigators turned to forensic science, hoping to determine if this was a botched robbery, or cold-blooded murder.

How did a stalker obtain the security system code for his victim's home? How did he steal her personal photographs? Police needed answers, and they found them in the most unlikely of places: the letters he wrote to frighten the victim and taunt those trying to protect her.

After inspecting storm damage to a home in Tampa, FL, the insurance assessor simply disappeared. Thirty hours later, her body was found in a nearby river. But the killer had been careless, using a murder weapon so unique and leaving behind clues so blatant that police would have no trouble tracking him down.

In 1997, Kelly Eckart's car was found with her belongings still in it, after working the late shift in Franklin, Indiana. Days later, her body was found in an isolated ravine. Tiny clues told police a great deal about the killer: he would own a car with olive-colored carpeting, a white blanket and distinctive bullets made from wax, not lead.

For twelve years, the murder of a young woman went unsolved, but with the passage of time came the development of technology. Would a used tissue found at the crime scene give police the evidence they needed to crack the case and bring a killer to justice?

When an off-duty policeman was shot dead, his fellow officers were determined to solve the crime. They needed clues to find the killer, and they discovered them in tiny fibres and an asthma inhaler.

The driver said he couldn't have hit and killed a pedestrian on a Harrisburg street. The Jeep Grand Cherokee he was leasing around that time had been sold months ago to a buyer in another state. Police were able to find the vehicle. They impounded it, took it apart, and discovered evidence, which would tell them what really happened that night.

In 1991, Grand Junction, Colorado is on edge after a series of deadly bombings which has killed 2 and injured one more and police race to find the culprit before he strikes again. Ultimately, it was the bombs themselves, along with the tools used to make them, which led investigators to the perpetrator.

When a little girl got sick and died, investigators were stumped. Was it an accident, an unexplained illness, or murder? Scientists would travel halfway around the world before finding the answer in two unlikely places: a shredded legal document and her mother's signature.