He was a recluse who spread terror through the mail for 18 years. Two men died and more than a dozen were injured , but Ted Kaczynski wasn't known as the Unabomber until his brother tipped off the FBI. Kaczynski's Manifesto, published in major newspapers, set off a flurry of activity for the FBI: writing analysis and comparisons, DNA gleaned from a single postage stamp and finally, Kaczynski's arrest at his tiny cabin. The agents collected enough evidence, including the Manifesto itself, to convict Kaczynski. He is serving four life sentences plus 30 years with no chance of parole.

A stranger snatched an eight-year-old girl as she played in her Tucson, Arizona neighborhood. Within hours, a drifter who was out on parole for abducting and molesting children, but he was nowhere to be found and time had run out.

Marine Captain Shirley Russell disappeared. FBI agents found her husband, himself a former Marine, was acting strangely. The FBI's intense investigation revealed a violent past.

Polly Klaas was kidnapped from her own slumber party and murdered, lasers helped the FBI identify and find the perpetrator. It took 200 FBI agents two months to find Richard Allen Davis, who was convicted and sentenced to death.

The body of 23 year old Robin Bishop was discovered near her car on a remote highway. After acquitted in two state trials, Gwaltney was convicted of the murder in the federal trial. The FBI was able to convince the third jury.

Thomas Dillon killed five outdoorsmen over a period of three years in rural Ohio. A mother's letter published in the newspaper addressing the murderer of her son prompted the killer to respond. Thomas Dillon was arrested and ultimately convicted.

A young mother and her two daughters were sexually assaulted and brutally murdered in Anchorage, Alaska. With only one piece of forensic evidence, a wash rag carrying pubic lice with which the killer used to clean himself, the FBI helped convicted the woman's nephew, Kirby Anthoney on all three counts of murders.

Two couples found themselves on the same deserted island paradise, but only one couple left alive. Buck Walker and Stephanie Sterns arrived in Hawaii on the Sea Wind, which belonged to the missing couple, Mac and Muff Graham. Years later, Buck Walker was convicted of murder.

The reputed boss of the Genovese crime family, Vince Gigante wandered the streets of New York wearing only pajamas and a bathrobe, but the FBI was convinced he was anything but crazy. The FBI helped convict Gigante of murder and murder conspiracy.

5-year-old Melissa Brannen disappeared from a Christmas party on Dec. 3, 1989, leaving behind a family wracked with anguish.

Claude Dallas lived the life of a cowboy -- a loner and distrustful of authority. When two game wardens confronted Dallas about his deeds, they were shot and killed. After a massive manhunt , Dallas was captured and convicted, but he escaped prison within months.

On February 26, 1993, an explosion rocked the World Trade Center parking garage. Six people died and more than a thousand were injured in the bomb blast which tore a 5-story crater in the building. Mohammed Salameh, Nidal Ayyad, Mahmud Abouhalima, Ahmad Ajaj, Ramzi Yousef and Eyad Ismoil were convicted and will spend the rest of their lives in prison.

By December 1985, John Gotti had assumed his place as the new Don of the Gambino crime family in New York with the assassination of his boss, Paul Castellano. When the FBI convinced Gotti's underboss, Salvatore Gravano , to testify against him, the jury came back with their verdict: guilty on all counts, including the murder of Castellano.

On June 21, 1964, three civil rights workers, who set out to educate southern blacks about receiving the right to vote, disappeared in Mississippi. The FBI gained the trust of an informant, whose information led to the conviction of seven local Ku Klux Klan members.

Posing as a fashion photographer, serial killer Christopher Wilder lured young women from shopping malls with promises of fame and fortune. Most ended up dead. national publicity that the FBI created led to the capture of the suspect.

A multiple murder-for-hire plot that was meticulously planned and executed. A mother, her 8-year-old son, and a live-in nurse were brutally murdered by an assassin. the FBI was able to zero in on Larry Horn, the father of the 8-year-old.

Young women were being abducted from their own front yards in broad daylight. The FBI was determined to put an end to the serial killer's deadly game of cat and mouse.

A young boy and his mother are kidnapped and murdered by a drug cartel.

The body of an unidentified young woman turned up on a highway in a small Pennsylvania town. Agents persisted to identity the body and to find the killer.

A Judge and his politician wife were brutally murdered in their home. The FBI uncovered a corrupt local government and a group of violent criminal conspirators.

Two brothers abduct a banker. FBI agents slowly pieced together tiny shreds of evidence.

A couple engaged in a gruesome crime spree that spanned six states and left eight people dead-including children.

A young mother and her infant son mysteriously disappeared from their home. A new DNA technique ended the mystery.

The FBI began a massive undercover operation designed to expose the Chicago Mafia's infiltration into the city's surrounding suburbs.

A series of brutal bank robberies and murders led to an exhaustive eight-month investigation by the FBI. What followed was the bloodiest firefight in FBI history.