The story of the hunt for one of the most notorious serial killers in recent American history--the BTK killer, who terrorized the Wichita, Kansas, area for years. After committing at least seven brutal murders, BTK (for Bind, Torture, Kill) vanished for over 25 years before sending clues of his crimes to the media in 2004. He continued to avoid capture until a forensic computer expert traced a computer disc that led investigators to a surprising suspect--a church president.

In this special 100th edition of Cold Case Files, we look at the biggest serial murder case in U.S. history - the 20-year hunt for the Green River Killer. Dave Reichert, the detective who made finding the killer his obsession, walks us through the case. He tells vivid, sometimes harrowing stories about the murders, saying, "You never forget the sight of a 16-year-old body lying on her back on the riverbank with ligature around her neck." Reichert headed up two Green River task forces until forensic DNA technology helped crack the case and brought him face to face with the killer thought to be responsible for 48 deaths.

When an adulterous church deacon is found shot to death in the back seat of his car, it looks like police may have stumbled upon a multi-party murder plot. And, a wife remains a key suspect in her husband's murder case for six years, until she takes the matter into her own hands to prove her innocence.

The dogged work of an Alberta, Canada, detective finally pays off when he tracks down the man who raped and murdered a 6-year-old girl 10 years earlier. And when police search for the killer of an 18-year-old hitchhiker, they find that the victim's diary is one of their best clues.

Law enforcement officials fear they may have to release a serial killer from prison until a 24-year-old murder case gives them a chance to lock him up for good.

A video tape made at an ATM machine helps police in Louisville, KY, to nab a man suspected of raping 13 women. And a DA investigator in Georgia helps crack a murder case that his father, a police chief, first worked on 30 years before.

This special edition of Cold Case Files offers an inside look, rarely seen, at an active cold case investigation. We follow Det. Vince Velazquez of Atlanta and Capt. Russell Popham of East Point, Ga., as they work to solve the 1995 rape and murder of 14-year-old Nacole Smith, one of Atlanta's most notorious unsolved crimes. We see Velazquez and Popham hit the streets to question people who might recognize the man in their composite sketch, and obtain DNA samples from potential suspects. "It's almost like the carrot's dangling in front of us, but we just can't catch it," Velazquez says of his painstaking, frustrating search for the killer.

Thirty-two years after the killing of University of Michigan law student Jane Mixer, police use DNA found on her pantyhose to finally track down the killer. And psychologists help solve a cold case by suggesting the lead detective take a page from the game of romance, and play hard to get with the killer.

On a summer night in 1987 a mother worries and waits for her 19-year-old daughter to come home. But Diana never comes home and she's found raped and strangled near the Hudson River. Investigators suspect her friend, Michael because his alibi is shaky and witnesses place his truck near the crime scene. Trouble is, he passes a polygraph and his DNA is no match. Nevertheless, Michael remains the chief suspect for 17 years, until DNA fingers another man who offers a chilling story of Diana's last breath. Then, a young family's life is shattered when a San Antonio interior design shop becomes a crime scene. In 1983, a young mother is raped and murdered at work. The crime remains unsolved for two decades. Then in 2003 detectives reopen the case pegging their hopes on DNA. But when the evidence turns up missing, detectives worry this case could be over before it starts.

Nine years after the murders of a mother and her teenage daughters, a wiretapped conversation between the suspected killer and his sister helps police to crack the case. And the baffling murder of a Virginia woman is solved when human bones are discovered by a geologist working in North Carolina.

Police in Albany, N.Y., get a surprise when a killer they think targets only older women is suspected in the murder of an elderly man. And the contents of a secret storage shed holds the grisly clues to a murder that has gone cold for more than 14 years.

A district attorney uses a clever technique--a "John Doe indictment"--to give law enforcement officials the time they need to track down the Schoolgirl Rapist from Rochester, N. Y. And prosecutors reluctantly decide not to prosecute their lead suspect in the rape and murder of a 9-year-old girl because they have only circumstantial evidence. But 12 years later, the cold case squad reopens the case, hoping DNA evidence will prove the supect's guilt.

A 14-year-old boy is charged with the murder of his sister, but his public defender believes the police coerced the boy's confession and that the real killer is still on the loose. And two deteriorated medical examiner's slides, made in a murder investigation 16 years earlier, give police the evidence they need to reopen the cold case and bring the lead suspect to trial.

A serial rapist seals his own fate when he sends a taunting letter to police, who use the DNA extracted from the saliva in the envelope's seal to track him down. And when a man is found dead in South Dakota, his head bashed in by a 50-pound rock, investigators go on a 20-year search for the killers--a man and woman who were part of a free-loving hippie group and are known only by the names "Outlaw" and "Inlaw."

Our cameras follow Detective Manny Reyes as he investigates the 1990 murder of a Fort Worth, Texas woman. Reyes talks to the woman's two sons, who believe that her husband, Bobby, was the murderer. We then watch as one of the husband's relatives tells Reyes that Bobby has confessed the crime to him. To make the case even stronger, Reyes collects physical evidence that connects him to the crime. Finally, Reyes meets Bobby for a dramatic interrogation. Will he crack and admit the crime--or will he hang tough and deny it all?

Bill Kurtis examines one of the most infamous cold cases in Los Angeles history -- the 1947 murder of actress Elizabeth Short, who was found nude and cut in half in an empty lot. Though charges have never been filed in the case, theories abound, and Kurtis investigates some of the most prominent ones. He talks to a retired LAPD detective whose 3 year investigation led to the stunning conclusion that his own father committed the murder. Kurtis also probes the theory that the killer was a surgeon named Walter Bayley. Kurtis finally explores the possibility that there may have been a police cover-up in the case to protect the real killer.

In Rhode Island, policewomen go undercover in as street walkers to nab the man suspected of murdering three prostitutes. And a dagger-shaped letter opener is the key piece of evidence that links a priest to the grisly 1980 murder of a nun in Toledo, Ohio.

After 19 years, Kansas detectives reopen the case of a banker found beaten to death in his bed--and the chief suspect is his cheating wife. And a man with a guilty conscience helps Arkansas police to crack a cold case of murder when he tells them that his ex-wife knows who the killer is.

After U.S. Navy sailor Andrew Muns disappears in 1968, the Navy claims that Muns went AWOL from his ship. But his sister works tirelessly for over 30 years to prove that Muns was really killed. And DNA surreptitiously gathered from a cigarette butt helps detectives to unravel a 20-year-old case of rape and murder.

DNA found on a marijuana joint in Florida in 2005 helps to solve the 1988 rape and murder of a California woman. And a cold case of murder in Illinois heats up when a jailhouse lawyer turns jailhouse snitch.

Detectives are baffled when two young girls are raped, murdered, and dumped in an abandoned house in Akron, Ohio. And a 26-year-old mother of three disappears on Christmas Eve in 1995, but the missing persons case goes cold when police can find few clues to her whereabouts.

The killing of a woman in a Virginia hotel room goes unsolved for a quarter of a century before investigators are finally able to zero in on the likely killer. And, when a 25-year -old women is shot to death during a jewelry store robbery in 1980, investigators collect fingerprints and blood from the crime scene. There are few leads and the case goes cold until 1999, when detectives test the blood evidence and develop a DNA profile. For two years more, that profile sits without a match, until 2001 when a convicted burglar is entered into the DNA databank.

Included: a man is suspected of killing his wife. Also: the case of a mother who vanished on Christmas Eve in 1995.

Guns found dumped in a pond outside of Atlantic City, N.J., help police to solve the 15-year-old murder of Detroit cab company owner. And the rape and murder of an Atlanta TV station receptionist goes cold for 20 years before the FBI's Combined DNA Index System (CODIS) links a man with three prior burglary convictions to the crime.

Looks at how law enforcers stick with cases for many years, using fresh evidence to win convictions or to free prisoners who were wrongfully jailed.

A detective in California tracks down a prostitute's killer with the help of a key piece of evidence--fingerprints lifted off two beer bottles found at the murder scene. And two persistent cold case detectives in Kansas City, Mo., use DNA analyses to investigate the 1990 murder of a woman and the death of a man killed in a car crash in 1988.

The Chicago Police Department launches the Women's DNA initiative to fund the testing of backlogged rape evidence kits and help rape victims find justice. Meanwhile in Sacramento County, California, the deputy district attorney hunts for the killer of a man who was brutally stabbed to death in his home 16 years earlier, using a new grant for DNA testing.