Two men were convicted of intentionally shooting and killing a passenger in a moving car, their friend was granted immunity for testifying against them, and the case was closed. Then a bomb exploded in the family home of the state's witness, instantly killing his father. Investigators turned to forensic science, hoping to determine if this was an act of revenge and if there was a way to link the two deadly crimes.

A serial arsonist was on the loose in Washington, DC. Each of the fires was started with the same type of incendiary device. The perpetrator was very careful and seemed to leave no evidence behind but there were clues in the ashes and it was up to forensic scientists to find them.

In 1957, California police searched for a man who had committed several crimes in one night – including murder, but after following thousands of leads, eventually, the case turns cold. Almost 50 years later, with advances in computer technology and handwriting analysis, investigators determine the killer.

Bombings are difficult to solve, because the perpetrator isn't usually at the scene, and the evidence goes up in smoke. But there are clues if investigators know where to look. In this case pieces of plastic the size of grains of sand, held the key to a man's murder.

When a fire destroyed most of a home and a young boy went missing, police organized the largest search in the history of their small town. First the boy's backpack was discovered five miles from home, and then his body was found 50 miles away. But the killer had been careless, and the evidence he left behind would lead police directly to him.

The decomposed body of a young woman was discovered in a Bakersfield irrigation canal. If there was trace evidence, it had been washed away. Another victim was found in that same canal a year later; this time, the perpetrator had been careless. The shoe prints found at the scene would lead police to the most unlikely of killers.

A behavioral profile is helpful in a murder investigation, but it's not a road map to the killer. One such profile caused the Baton Rouge Police Department to search for the wrong man. They might not have made an arrest, had it not been for a DNA picture of the suspect, painted by a molecular biologist. [also marked as S10:E15]

Police initially suspect that the death of a gay student is a hate crime, until just three strands of hair and some microscopic cells help them unravel a web of lies, and to find the real motive for the murder.

When a woman's husband was gunned down in his own garage by intruders, investigators worked tirelessly to find the assassins. But when they discovered that a wound sustained during the attack by the grieving widow may have been self-inflicted, they turned to science to help them unravel a twisted tale of lust, greed and deception.

When Genell Plude was found dead in her bathroom, the scene pointed to suicide. But a coroner's inquest and a unique application of forensic science gave investigators a different explanation for her death. It was a theory which, if true, could turn her husband Doug into the prime suspect.

Emergency dispatch received a call from a man who said his girlfriend shot and killed herself. Police found the victim in the caller's house, lying in a pool of blood with the gun next to her on the floor. The autopsy revealed that the gunshot wound was not self-inflicted and the evidence found on her body would give police a golden opportunity to catch her killer.

When a popular disc jockey was found murdered in a community garden, police swung into action. A sniffer dog and a blood spatter expert led police to the killer and he'd been much closer than they realized.

A 29-year-old woman was killed instantly when a bomb exploded in her home. The device was so powerful that shrapnel was embedded in houses across the street. The bomber had not only knowledge and skill, but also a motive for murder.

A killer tried to incinerate and destroy everything that could link him to his crime. But in doing so, he inadvertently created new forensic evidence, evidence which came to light with a technique never before used in a criminal investigation.

A man riding a bicycle was fatally injured, the victim of a hit-and-run accident. Tiny clues found at the scene created a picture of the vehicle which struck him and led police to its driver.

A mother of two young children was found dead in her bedroom. It appeared she had killed herself: There were suicide notes near her body, and a pistol was in her hand. Her death was ruled a suicide – but when investigators learned she had almost died in a house fire three years earlier, they decided to take another look at the evidence.

The wife of an Air Force officer was found dead in her bed, with a plastic laundry bag near her face. At first glance, it appeared she'd been doing laundry, fell asleep, rolled onto the bag, and suffocated. But further investigation proved that the scene had been staged. Her death wasn't an accident; it was cold-blooded murder.

A highway patrolman was dispatched to what he thought would be a routine traffic accident until he looked in the car. While he had no formal training in forensic science, he had seen hundreds of accidents – but never as much blood as this. He was shocked by the coroner's ruling of accidental death, and then an anonymous phone call breathed new life into his investigation.

A Native American woman was brutally killed in the desert of New Mexico, and the crime scene was rich in forensic evidence: tyre tracks, shoe impressions and even the murder weapons. The site was less than 10 miles from another crime scene where, two years earlier, a male Native American was beaten and stabbed to death. Police began to wonder: was a serial killer on the loose?

When the head chef of a historic Philadelphia restaurant was found dead, investigators interviewed the usual suspects: family, friends and coworkers. As they sifted through the evidence, police uncovered a chilling tale of debt and deceit.

An obstetrician returned home from the hospital and found his wife on the floor of the bathroom. She was covered with blood and not breathing. He tried unsuccessfully to revive her, staining his clothes with her blood in the process, and then he called 911. His version of events was not supported by the blood spatter evidence, and investigators had to determine why. [also marked as S10:E17]

When police recovered the submerged car of a man reported missing, they expected to find his body – but it wasn't there. His broken eyeglasses were on the floor of the vehicle and the interior was coated with motor oil. The investigation which followed would uncover an obsession turned deadly, and the motive for murder. [also marked as S10:E19]

The murder of an eccentric millionaire was not entirely unexpected; he flaunted his wealth and cared little for personal security. The evidence at the crime seemed to indicate robbery, but investigators wondered if there was something more.

In an affluent suburb of Philadelphia, police were called to the scene of what appeared to be an accidental drowning. The investigation gradually focused on one person, a suspect who had more than a million reasons to want the victim dead.

When an elderly couple died in a suspicious house fire, their son became the prime suspect. The son insisted he was innocent; he said he tried to extinguish the fire by pouring water on it, but that only made it worse. Investigators turned to forensic science to determine if the fire had been set deliberately, or if it was an unfortunate accident.