When a young girl was found dead, police quickly arrested the most likely suspect. But cutting-edge technology from NASA enabled a forensic odontologist to prove the wrong man was behind bars. With the killer still on the loose, the investigation was far from over.

It's usually easy to determine how a criminal entered the crime scene. But in this case, it was far from clear. It looked like the killer vanished into thin air...and perhaps he had.

When a young fireman died from what appeared to be serious but undiagnosed heart disease, his family and friends were devastated but they had no proof of foul play. Then they learned that, six years earlier in a nearby town, a young police officer died in the same way. The men had one thing in common: at the time of their deaths, they were married to the same woman.

Security cameras in a casino tracked a young woman's movements until shortly before she disappeared. She was never seen again, but through the evidence she left behind, she was able to tell investigators what happened to her and who was responsible.

It was one of the most unusual cases in forensic history. Investigators had to find a way to solve a murder case with evidence which consisted of a squashed tomato found at the crime scene, and tiny, pinpoint reflections of light in a photograph. Would it be enough to catch a killer?

When a dedicated, well-respected teacher disappeared, police had to determine if she'd gone on vacation without telling anyone, or if she was the victim of foul play. Investigators turned to forensic science, hoping to find the answers they needed.

Seattle police had no suspects in the violent murder of post-grunge singer, Mia Zapata. More than a decade would pass before the evidence collected by an extraordinarily prescient medical examiner could be used by forensic scientists to identify the killer.

A Michigan State University grad student disappeared and was presumed dead. With the help of a professor of geological sciences, police hoped to get the "dirt" on her killer.

How unlucky could one man be? His wife had taken her own life, and his college sweetheart had killed herself in much the same fashion fourteen years earlier. Investigators had to determine if this was a bizarre coincidence, or an attempt to get away with murder... twice.

In 1996, 54-year-old Gayle Isleib was ambushed in her Manchester, Connecticut driveway and shot to death. During their investigation, police learned that her 25-year-old co-worker Tyrone Montgomery was in love with her and that she had spurned his advances. They now had to determine if love had turned into obsession... and a motive for murder.

The victim had been sexually assaulted and stabbed to death on the beach, just ten yards from the hotel where she was staying. A pair of men's tennis shoes was discovered near her body. Police were sure that if they found the man who fit the shoes, they would also find the man who committed the crime.

A 13-year-old girl went missing from her Colorado home, and the only evidence the kidnapper left behind was three fingerprints on a window screen. Two years later, a latent print examiner, new to the county and the crime lab, changed the course of the investigation by sharing a little-known fact with his colleagues.

A brutal murder, lots of suspects, and conflicting evidence but the forensics were clear on one thing - the killer knew his victim and that alone gave investigators a head start.

A serial killer was on the loose and police had to find him before he struck again. Their most promising lead was an unusual one: a bloody fingerprint on the body of one of the victims.

On Halloween night 2004, Adriane Insogna and Leslie Mazzara were brutally murdered in their Napa, CA, home. The killer was not seen by their downstairs roommate, but he left his DNA behind in some cigarette butts and a groundbreaking test revealed his race and even the color of his eyes and hair.

After the suspect was convicted of arson and murder, he steadfastly maintained he did not commit the crimes, but he was sentenced to a minimum of 25 years in prison. He had no money, no lawyer and only a fifth grade education, but he never gave up. He turned to the law books in the prison library and television programs about forensic science, and set out to prove his innocence. [also marked as S12:25]

A woman was brutally murdered in her home, and the only witnesses to the crime were the family dogs. An expert in canine behavior was convinced the killer knew both the victim and the animals, and he was determined find out exactly what the dogs had seen.

The killer probably hoped to cover his tracks by staging the crime scene. But investigators saw through the attempt almost immediately, and they turned to forensic science to learn what really happened that night. [also marked as S12:E19]

A 6-year-old girl ran and hid when she saw her grandmother being beaten to death, but the man followed her, beat her and assaulted her. The girl said he was her Uncle Clarence, and he was convicted because of her identification. She recanted her testimony years later, but the court denied Clarence's petition for a new trial. His wife was convinced he was innocent, and decided to conduct her own investigation to prove it.

In 1984, the body of college co-ed Laura Salmon was found on a Georgia farm, covered with her own denim jeans as well as the jeans of the killer. Investigators had plenty of suspects, including former boyfriend David Kyle Gilley, but no conclusive evidence linking any of them to the crime. More than a decade later, sophisticated technology would breathe new life into a case grown cold with the passage of time and implicate her killer.

The body of an attractive young woman was found a mile from her abandoned car. Police were especially concerned when they realised the victim had come to them for protection just two weeks earlier, after a road rage incident. Concern turned to dread when the evidence began to point not to an aggressive driver, but to one of their fellow police officers.

In 1969, 25-year-old phone operator Diane Maxwell is raped and murdered by a black man. Her brother promised he'd find out who was responsible and bring the killer to justice. It would take more than thirty years, but the young man kept his promise and, in doing so, brought closure to his family.

The crime scene was especially violent: A husband and wife had been shot to death in their bedroom. At first, investigators thought their 16-year-old daughter was lucky to have escaped unharmed... but after a while, they wondered if the reason she was alive had more to do with careful planning than good fortune.

A young, attractive hairdresser was sexually assaulted and murdered in her own beauty salon. The evidence at the crime scene didn't match any of the suspects and, after the initial investigation, the case went cold for ten years. Then a witness who had been silent for more than a decade decided to do the right thing.

A human skeleton was discovered in the North Carolina marshlands and, when investigators learned she'd been dead for 18 months, they knew it would be difficult to find out who she was, much less who killed her. A forensic anthropologist was able to determine the victim's race, age and height, but it would take an inventive computer consultant to give her a face and a name.

After shooting his victims in the head, the killer staged the scene, placed the incriminating evidence into a plastic bag and tossed it into the river. Instead of floating downstream, it became entangled in overhanging branches. Days later, when police found it, they hoped clues to the killer's identity and the solution to the crime were "in the bag."

In a tragic twist of fate, just days after the woman sold her home and moved to a modest trailer, a fire took both the trailer and her life. But the autopsy proved this was no accident. It was arson and murder. Investigators had to determine who wanted the woman dead... and why.

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.

A college senior was found raped and murdered near an unpaved footpath used by students to walk from one side of campus to the other. Five years earlier, a student was assaulted and killed in her off-campus apartment and, a year after that, another student was killed in almost the same way. Police feared a serial killer was on the loose and they needed to determine what – or who – these women had in common.