In major criminal cases, informants can be worth their weight in gold. Armed with knowledge only an insider could possess, one informant has the power to topple an entire criminal organization. While some crooks go turncoat after a change of heart, others are just looking out for themselves.

Use their testimony as currency, criminals can walk away from a life of crime and retribution with essentially a slap on the wrist and a brand-new identity.

Shocking? Well, when given the choice of prosecuting a single person or taking down the whole group, it becomes less so. Whether these canaries are singing for justice or just trying to stay out of the cage, they're responsible for helping to clean up the streets.

From money to murder, we've assembled some of the most scandalous cases to rock the news.

By Tiffany Champion
Posted 25 July 2013

Tommaso Buscetta was involved in the Sicilian mob's expansion into trafficking heroin to the United States. Arrested in 1984, he gave investigators in-depth dirt on organized crime in Italy.

For the first time, officials were able to prosecute the Mafia as an institution in the 1987 MaxiTrial. At the end of the nearly two-year trial, most of the 450 defendants received guilty verdicts.

Buscetta also appeared in U.S. courts, testifying that the American mob bought heroin from the Sicilians and sold it out of pizza restaurants, leading to the trial's nickname of "Pizza Connection." His testimony earned him U.S. citizenship and witness protection.

In 1940, 34-year-old Abe Reles had already been arrested 42 times and served six prison terms. In jail for murder, he decided to turn informant. As a member of Murder Inc., a crime syndicate specializing in contract killing, Reles was able to provide details on 70 known unsolved murders, as well as hundreds more.

Reles and the other informants in the case were under 24-hour police protection waiting to testify when he fell to his death from the window of his room.

Whether Reles jumped or was pushed is unknown to this day, but his fall led to his post-mortem nickname of "The Canary Who Could Sing but Couldn't Fly."

According to The Wall Street Journal, Noah Freeman and Donald Longueuil were close friends and inside traders. Even though Longueuil was Freeman's best man, the latter was quick to cooperate with investigators in order to avoid jail.

In 2010, Longueuil learned that the firm that used to give them insider tips was being probed. Panicking, he tore apart a hard drive with incriminating evidence, throwing the pieces into different garbage trucks around New York.

Approached by investigators, Freeman agreed to record Longueuil discussing their illegal trading activities and the way he had disposed of the evidence. With the information Freeman provided, prosecutors were able to charge Longueuil, sentencing him to two and a half years.

Though Freeman is still awaiting sentencing, at his plea hearing he was granted permission to travel to Puerto Rico and the U.S. Virgin Islands to compete in triathlons with his wife.

Joseph Massino became the boss of the New York Bonanno family in the early 1990s. Following his arrest in 2004, Massino broke the mob's code of silence, giving law enforcement details on hundreds of organized crime members and recording conversations about past and planned contract killings.

In exchange for his assistance, Massino was taken off death row and given two life sentences.

In 2011, he became the first New York boss to take the stand. His testimony led to the prosecution of 10 criminal cases. On July 10, the U.S. Attorney's Office in Brooklyn asked for a reduction of his sentence, and Massino was given time served (10 years).

Kenneth Robinson, Matthew Kluger and Garrett Bauer ran an insider trading scheme for 17 years.

It took Robinson just days to start talking after federal agents approached him with evidence of his guilt. For that, he received just 27 months in jail. Bauer and Kluger were sentenced to nine and 12 years, respectively. Kluger's is the longest sentence ever for insider trading.

This story almost played out very differently. Kluger told Bloomberg that he considered turning in the others shortly after the scam started.

To add insult to injury, he got the smallest cut of the three, in addition to the longest sentence. He had been under the impression that the three split the profits evenly but later learned that Bauer kept most of the money for himself. While Bauer took home about $32 million, Kruger didn't break $1 million.

In 2007, the Securities and Exchange Commission approached Roomy Khan about her involvement in insider trading with Raj Rajaratnam. Khan worked for him at Galleon Group, the hedge fund that at one point was worth $7 billion.

Facing charges of conspiracy to commit securities fraud, securities fraud and lying to the FBI, Khan cooperated. The information she provided gave law enforcement the grounds to wiretap Rajaratnam's cellphone.

Those recordings played a central role in the shocking trial of Rajaratnam for conducting the largest insider trading scheme in U.S. history. Rajaratnam was ordered to serve 11 years in prison, pay a $10 million fine and forfeit $53 million that he gained from the insider tips.

Khan received one year in prison, a stiffer penalty than the five years' probation her attorneys sought.

Opposed to the methods of his boss, Sammy "The Bull" Gravano turned informant in 1991. He was the first underboss to turn on his own family—the Gambinos, in his case.

Gravano's information brought down almost 40 mobsters. In return, authorities overlooked his confession to committing some 19 murders, and Gravano got a sentence of just five years.

Released into witness protection, he decided to leave the program and move to Arizona, where he got involved in a multimillion-dollar ecstasy ring. Gravano is now serving a 20-year sentence.

Frank Lucas ran Harlem's heroin business in the 1970s. His empire was brought to a halt when prosecutor Richard Roberts caught onto the scheme in 1975. A year later, Roberts had enough information to put the kingpin away for 70 years.

Instead, Lucas became an informant and worked on more than 100 narcotics cases. His sentence was reduced to five years, and he was able to leave with time served. Lucas left witness protection and returned to his old habits. In 1984 he was back in court facing narcotics charges.

This time, Roberts was Lucas' defense attorney and got the sentence reduced to seven years. The two remain friends. Their story was the subject of the 2007 film "American Gangster."

Mark Felt was associate director of the FBI in 1972 and 1973. He opposed the Nixon administration's attempts to stall an investigation into abuses of power, so he fed insider information to Washington Post journalist Bob Woodward under the pseudonym "Deep Throat."

If Woodward wanted to talk, he would move a flowerpot with a red flag to another spot on his balcony. If Felt had information, a circle would appear on page 20 of Woodward's home-delivered copy of The New York Times.

The meetings fueled the Post's scoops of the Watergate scandal. Felt remained anonymous until his identity was revealed in Vanity Fair in 2005.

Abraham Shakespeare won millions in the Florida lottery and lost it just as quickly. After he disappeared, investigators turned their attention to the woman who stole his money, Dee Dee Moore.

She recruited Greg Smith, a friend of Shakespeare's, to make phone calls pretending to be the missing man in order to get the police off her trail. Instead, authorities tracked down Smith, who became an informant.

Smith outfitted a Red Bull can in his car with a recording device and got Moore on tape orchestrating cover-ups for the disappearance. In the midst of these tapes, she reveals that Shakespeare is dead and buried in the backyard. Moore is serving a life sentence for first-degree murder but maintains her innocence.

To hear the whole story, watch the episode of American Greed.