Sometimes, the wrong people are punished for crimes they did not commit. Forensic scientists use DNA analysis to overturn convictions of these innocent men and women who have spent years behind bars.

Forensics in the O.J. Simpson Murder Trial: The verdict is in Not Guilty of murder. O.J. Simpson emerges a free man. What was the evidence and could it be trusted? These experts break down the evidence could and could not tell us.

A house fire in California turns into a murder investigation when authorities discover that the victim’s best friend and personal manager had recently cleaned out her bank account.

Marriage is one of the tightest bonds two people can have, until lies and deceit drive one of them to kill. In this episode, forensic experts are employed to link a woman’s husband to her violent murder and uncover a murder disguised as an accident.

Often, a killer will build the victim’s trust before he or she attacks. In this episode, New Mexico police search for a missing teenager who disappeared from a local skating rink. Authorities suspect the two friends she was last seen with.

It is difficult to convict a murderer if the body can’t be found, but forensic science is finding ways to do it. A speck of blood, a piece of a fingernail or a strand of hair may now be enough evidence to prove a murder and capture a killer.

Often, murderers will change or stage a crime scene, turning murder into suicide, pinning blame, or hiding the body completely. However, forensic investigators can detect masterful disguises and the truth can be found from clues at the scene.

As technology becomes a bigger part of our lives, it’s becoming difficult to do anything without leaving behind an electronic trace. Cell phones and ATMs track our every move. When it comes to solving murders, this isn’t necessarily such a bad thing.

Advancement in science and technology are encouraging people to revisit the past in hopes of answering questions that have remained unanswered. Techniques from the 20th century are applied to cases dating back as far as ancient times.

Plants help provide oxygen and nutrients for existence. In criminal investigations, a simple seedpod can provide the missing link by placing a suspect at a crime scene. Dirt left on shoes, tires or clothes can pinpoint a crime scene.

Forensic psychologists delve into the minds of serial killers, explaining why, most often, they can be a friendly neighbor or a tenacious co-worker – the ones who hide their darkness better than anyone else.

No crime scene is absent of clues. No matter how chaotic or how clean it may appear to be, the culprit is bound to leave something telling behind. Sometimes it’s nothing more than a fingerprint or shoe tread. Sometimes that’s all that’s needed.

Because of new technologies, terrorism is a growing international threat. With the expertise of bomb squads, chemists and tool mark experts, bombs are deactivated and criminals are caught.

Insurance torchings, mob burnouts and arson murders: these crimes are designed to take all clues with them. But a case can be built from ashes. Arson investigators do everything from gathering physical evidence to mounting undercover operations.

Missing Person: In America nearly 1.8 million people are reported missing each year, factor in the world and that number triples. Using computer databases and other means victims are found, laid to rest…or never seen again.

Investigators are always on the cutting edge of new forensic techniques that can help them solve cases more accurately. Advanced techniques allow crime solving to take on a new dimension, providing safer and more efficient ways to capture criminals.

A tool used to commit a crime can often be the same tool used to solve it. The pattern a machine leaves on an item, the unusual way a tool crimps a wire and even something as innocuous as the shape of a wood chip can lead to a killer.

While drugs can cure disease and ease pain, they can also be agents of murder. Toxicologists can examine blood and tissue to uncover cases where death is not as natural as it may seem – from slow arsenic poisoning to quick cocaine overdoses.

Identifying Burned Remains: Murder is hard to prove with no body, when the victim has been burned it is even more difficult. Fire does more than destroy evidence . . . it can keep the secrets you don’t want anyone to know.

With DNA analysis just a few microscopic cells found at a crime scene can be used to convict a killer. Forensic scientists can analyze droplets of blood, hair fiber, or a piece of chewed gum to determine the identity of a victim or killer -- or to prove innocence.

Sometimes those closest to a victim can be the most dangerous. Beneath a layer of trust can lurk a deadly obsession. In these cases, authorities employ an arsenal of forensic techniques to uncover the twisted path of lies that leads to murder.

Murdering a child is perhaps the most heinous of crimes. But no matter how defenseless a killer believes a young child to be, there is no hiding from the clues left behind.

Every family has its secrets and sometimes blood relations lead to bloodshed. When murder becomes a family affair, investigators must turn to science to uncover family plots.

Observing how the smallest bits of forensic evidence, such as carpet fiber or an eyelash, can seal a case. Included: how strands of hair indicted a killer.

Young men shipped off to war would never return. Forensic experts work to tell their stories.

Journey into the dark recesses and calculated madness present only in our worst nightmares; and in the minds of serial killers, such as Richard Chase - The Vampire Killer of Sacramento, Mike DeBardeleben - The Mall Passer, and John Wayne Gacy - The Killer Clown, to name just a few. Renowned FBI profiler Robert Ressler can reveal unseen clues about a killer simply by learning details about the crime. Investigative profiling discloses a killer's hidden motives.

When murderers hide or destroy the remains of their victims, forensic scientists must reconstruct the scenes and prove murder for an absent witness.

Sometimes the cause of death does coincide with the scene of the crime. When an untraceable poison is used as a murder weapon, investigators rely on forensic toxicologists to follow a killer’s tracks and expose a toxic death.

Accidental deaths, suicides, disappearances and fires: they’re an everyday part of an insurance investigator’s job. But these cases shouldn’t be taken at face value. Forensics has become a vital tool in exposing insurance fraud.

Some people murder for love, others murder out of hatred. But sometimes people kill for the money. When greed is the motive, investigators must make every clue pay off in these murder-for-profit cases.

Scientists explore the differences between targeted and random poisoners, and the significance of disguising a targeted act of poison as a random act, such as the Tylenol case in Chicago.

Often killers are careful to not leave any fingerprints behind. But the methods of the murder itself can leave a lasting impression on authorities, especially when the tools of a killer’s trade leave a victim marked for death.

Poison is the subtlest murder weapon and poisoners are sometimes the most brutal killers, harming their victims over time to disguise the murder. Investigators must see through the unusual circumstances to bring these murders to light.

Some people don’t care who they kill; they just want to hurt innocents. Bombers, snipers and spree killers: these murderers are the hardest to catch because they have no connection to their victims, people in the wrong place at the wrong time.

Sometimes blood relations lead to bloodshed. When money is the motive, murder can rip at the very foundation of family and marriage. When homicide becomes a family affair, investigators must turn to forensics to shed light on these crimes.

Even the most puzzling cases can be solved with the tiniest of residue left behind at the crime scene. Trace evidence and paint analysis can be used to track down a serial killer or dog hair can be used to link separate murders to a single suspect.

Drowning deaths often look like accidents and over time water can destroy the few clues the killer may have left behind. Investigators must turn to forensic science to solve homicides in which the victims were found in bodies of water.

A dog can be a dead man’s best friend. Some dogs have been trained by law enforcement to sniff out corpses, drugs, explosives and missing persons. Even with advances in science, a dog’s nose is often first to find fundamental clues.

Forensic scientists find clues written in blood as they investigate the murders of three women who were killed by men who once loved them.

For the forensic entomologist, insects that nest in corpses are like witnesses to the crime. By studying their behavior, scientists learn everything -- from when a murder was committed to what sort of weapon was used.

For some killers, murder can be a lucrative business. When a victim has been targeted for death, investigators must dig deep and go beyond the obvious to uncover a murder for hire.

A murdered woman is found stuffed in the boot of her car, and a routine investigation reveals a wife may not have abandoned her family on purpose. When everyday substances reveal hidden clues that break a homicide case, those substances become the elements of murder.

Most victims are meticulously chosen by their murderer because of a connection or because they match a set of criteria. The most terrifying cases of murder occur when the killer appears to choose victims at random.

Killers often will try to cover up their crime by hiding the remains of their victims. Sometimes bodies may lay hidden for years before they are discovered. That’s when forensic scientists are called upon to reveal buried clues.

When a victim is killed at point-blank range, police often suspect that a friend or acquaintance is to blame, because for a stranger it would otherwise prove too difficult. Investigators must use the clues to track down the most unlikely killers.

In most murder cases, police rely on motive to pursue a killer. But when the murderer is a stranger, the crime may go unsolved for years. Investigators must employ an arsenal of forensic techniques to trace these seemingly random lethal encounters.

Some killers choose to hide their victims and investigators must then rely on forensics to uncover proof of murder. From identifying remains to uncovering post-mortem clues, medical examiners are integral in solving some of the most brutal crimes.

At a crime scene, anything left behind or moved out of place is considered a clue. But a fire can extinguish everything in its path, challenging forensic investigators at every turn.

When victims of murder knew their killers, they can be caught off guard. The killers rely on their intimate knowledge to pull off the perfect crime. But even the best-laid plans leave traces of the forsaken trust.

Coroners play a vital role in piecing together the final moments of someone’s life. Los Angeles County coroner Julie Wilson provides an in-depth look into the science of death, as well as the techniques and methodology used by coroner investigators.

Approximately 1.8 million Americans are reported missing each year. Some are runaways who eventually find their way home but others simply disappear without a trace. When foul play is suspected, investigators turn to forensics to find the missing.

Often, the witnesses of a crime are also the main suspects. They’re able to manipulate the truth to throw off the authorities. When a murder is committed and deceit clouds the evidence, investigators turn to forensics to uncover the truth.

A simple clue can provide the missing link by placing a suspect at the scene of the crime. Dirt left on shoes, tires or clothes can pinpoint where the crime occurred. It takes the skilled eye of a forensic investigator to follow the trail.

Sometimes, seemingly small and insignificant clues – three hairs, microscopic fibers, a paint chip – become a victim’s silent witness and help solve even the most baffling of cases.

When abduction turns to murder, forensic science is a vital key to finding justice for the victims of a kidnapper’s deadly intentions.

The tread of a tire, a single shoe print or even the shape of a bruise can help investigators track down murderers.

The elements of nature can reduce a body to bones in a matter of weeks. Combining art and science, forensic anthropologists can give victims a face long after they’ve been forgotten.

When teenagers are driven to kill, their victims are not the only ones to suffer from their violent crime. In three such cases, the families of the killers and their communities become victims of these young criminals.

When money is the motive, there is no limit to what a killer will do to get away with their fortune. When officers find the dismembered remains of a young man, they also discover his girlfriend recently took out an insurance policy on the deceased.

Sometimes, cooperation from people who are not associated with a crime in any way is the only link between a criminal and the clues left behind for forensic experts. This episode examines cases in which good Samaritans help solve puzzling crimes.

When there’s a difficult case to crack, agents of the Bureau of Alcohol, Tobacco and Firearms can be called in to help. These investigators have the means to tackle crimes involving drugs, arson and weaponry.

Fingerprinting: The backbone to forensic science, the fingerprint is a very effective way to identify victims and criminals. Not only are fingerprints used but also palm prints and foot prints. Data entered into massive databases make identifying people easy…when there is a hit.

Black Boxes: A plane plunges toward the ground and upon impact little remains. The only possible survivor is the flight data recorder. This little black box could hold the answers to the last terrifying minutes.

There’s an old saying that a burden shared is a burden halved. But when people team up to commit murder, the weight of their guilt remains just as heavy. Investigators must rely on forensic science to capture partners in crime.

What does it take to prove murder if the victim cannot be found? Forensic investigators must go to great lengths to catch the killer when the victim is only presumed dead.

For homicide investigators, it’s a race against time when they track their deadliest foe: a serial killer who murders to feel alive.