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.

When a woman went missing, friends and family were determined to find her. Their worst fears were confirmed weeks later when her body was discovered. Blood evidence and computer forensics helped investigators to catch the killer, and convince the jury of his guilt.

The woman could have lost control of her SUV on the icy road, and plunged down an embankment into a shallow creek. But there were footprints in the snow leading away.

A successful stockbroker told his wife he'd be working late, and when he didn't come home, she reported him missing. Investigators found his car a few blocks from his office and, two days later, proof that he had been murdered.

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.

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.

A car was found in a drainage ditch and the bodies of a man and woman were inside; both had been shot to death. The car windows were broken and shattered glass should have been everywhere, but it wasn't. A fingertip torn from a latex glove would point investigators to both the crime scene and the killer.

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 who was known to have suffered from depression apparently took her own life. But her sister told police that, a year before her death, she said if anything were to happen to her, there was a note in the china cabinet. Investigators found the note and the killer.

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.

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.

One warm summer afternoon, the town of Verona, Wisconsin, faced its first triple homicide. To solve the case, investigators had to delve into the world of high rollers and offshore betting.

The body of a young girl was discovered on isolated farmland near Delano, California. She had no ID, but police found mailbox and house keys in the pocket of her jeans. With no other clues, they checked the mailboxes of every apartment building in Delano and their persistence paid off.

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.

The medical examiner ruled the death an accident, but the detectives investigating the case thought the evidence at the scene indicated otherwise. It would take three years, an exhumation and a second autopsy to determine who was right.

When a hit-and-run boating accident caused the death of a popular young man, investigators faced the daunting task of searching for one boat among 1200 others. They asked anyone who had seen the accident to come forward. The man who responded did much more than witness the crash; he was a passenger in that other boat.

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 1993, 82-year-old Kathryn Bishop was found dead in her Pennsylvania home. The evidence at the scene indicated that the perpetrator had been running out of the house, not breaking into it. Tiny clues on the victim's body would tell police what happened that night, and who was responsible.

A wealthy man and his wife were attacked by three men outside their luxurious Louisiana home. He was shot dead and she was forced to open their hidden safe. The woman could not describe the men because they wore masks. To solve the case, police would have to find out who knew about the concealed safe, and who would benefit from the crime.

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.

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.

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.

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.

The victim had ingested a massive amount of cyanide. An unlikely clue – a flaw on a mailing envelope – exposed a murderer who was willing to kill innocent

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.