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.

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.

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.

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.

The law enforcement agency of the United States Navy and Marine Corps uses forensic science to solve perplexing murders and fulfill their motto: “To the living we owe respect; to the dead, we owe the truth.”

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.

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

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.

Ballistics: A body with a gunshot wound to the head, the gun is next to the body. Was it suicide or murder? Every part of the gun can be analyzed for the correct answer.

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.

Philadelphia’s Vidocq Society, named after an 18th century French detective, is one of the world’s most unusual crime-solving organizations – a members-only club made up of forensic professionals. Witness these sleuths solve impossible cases.

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.

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.

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.

For some killers, once is never enough. Often, cold and calculated serial killings are more difficult to solve than violent crimes of passion. For investigators, the challenge is steep when the killers murder by numbers.

Lies, deception and contradicting witnesses can often throw investigators off the trail of justice. But when indisputable evidence refutes a killer’s story, police must use the clues to piece together the truth.

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.

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

Explosives Investigations: A woman opens a box which explodes killing her. Soon to follow are five other bombs just as deadly as the first. This soon turns into a massive investigation leaving the experts to sift though the evidence.

A good coroner can deliver what is necessary to solve a crime, while a bad one can destroy an otherwise solid case. Two of the country’s most respected coroners provide an inside look into their jobs, sharing their insights into crime solving.

When a killer turns a gun on a victim, ballistic analysis is key to cracking the case. Each shot fired leaves behind its own clues, allowing scientists to target murderers with deadly aim.

Anytime, anywhere, people disappear – and sometimes these disappearances end in tragic murder. Kidnappers always leave clues behind, but chasing them takes time, hindering investigators’ attempts to solve these fatal abductions.

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.

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.