In the early 1920s, discovery of oil under Osage land in north-central Oklahoma made members of that tribal nation among the wealthiest people in the world. By 1923, the Osage people were sharing what amounted to $30 million in royalties. But scores of those wealthy Indians began dying—in mysterious shootings, stabbings, explosions and suspected poisonings. Out of inertia, indifference or corruption, local law enforcement did nothing.

Members of the Osage turned to Washington for help, appealing to what was still known simply as the U.S. Bureau of Investigation. Under the leadership of a young, untried J. Edgar Hoover, the Bureau used undercover informants to identify some of the white Oklahoma residents who had tried to marry—and murder—their way to oilfield riches. Agent Tom White, a former Texas Ranger, led the investigation, which ultimately convicted William Hale, a prominent cattle baron, his nephew Ernest Burkhart and others in a vast conspiracy. Many other Osage homicide cases from the era remain unsolved.

On the evening of March 1, 1932, one or more kidnappers abducted the toddler son of famous aviator Charles Lindbergh. They left behind a ransom note demanding $50,000, some muddy footprints and a broken ladder. Two months later, the boy’s broken and decomposing body was found partly buried near the Lindbergh mansion.

The next day, President Herbert Hoover directed the Bureau to coordinate the murder investigation. Crucially, special agents flooded the region with notifications of the serial numbers of the gold certificates paid as a ransom. More than a year later, a German immigrant carpenter named Bruno Hauptmann used one of these to buy gas at a service station. After his arrest, another $13,000 worth of the securities were found in his garage. When Hauptmann stood trial, Bureau agents testified that his handwriting matched that of the ransom note. He was convicted in 1935 and executed in the spring of 1936.

When the infamous crime spree of Depression-era outlaws Bonnie Parker and Clyde Barrow ended in a barrage of gunfire, it was local police officers who staged the ambush. But it was the Bureau that helped those officers determine just where to lie in wait. By May 1934, when the couple were linked to stolen cars transported across multiple states, prompting federal involvement, Parker and Barrow were already responsible for a series of brazen robberies and murders across a large swath of the United States. Eventually, Bureau agents in at least eight cities would collaborate with law enforcement in as many different states, sharing tips and fresh leads. The pursuit prompted early Bureau efforts at profiling, as special agents tried to anticipate where Bonnie and Clyde might be heading next. Ultimately, it was an FBI agent who tracked them to a remote corner of Louisiana where the successful ambush took place.

As the Cold War heated up in the late 1940s, U.S. military intelligence agents working to decode Soviet “diplomatic” cables made a stunning discovery. When they finally cracked the cypher, messages revealed a spy network burrowed deep inside America’s top-secret atomic development program at Los Alamos, New Mexico. FBI agent Bob Lamphere, who supervised numerous high-profile Cold War espionage investigations, followed the trail of clues in these decrypted messages, tracing the links that led from Los Alamos scientist Klaus Fuchs to a nondescript engineer named Julius Rosenberg in New York.

The FBI interrogated and arrested several members of the spy ring, including Julius and his wife Ethel. FBI head Hoover, who declared the Rosenbergs guilty of the “crime of the century,” clearly viewed their 1951 conviction as justice. But it also was controversial: Later revelations show that the FBI only pursued the case against Ethel in order to make Julius confess. Neither did; both were executed in 1953.

Almost as soon as the fatal bullets were fired in Dealey Plaza in Dallas on November 22, 1963, the FBI took a lead role in investigating President John F. Kennedy’s assassination. FBI agents responded to the scene, interviewed witnesses and preserved whatever evidence they could find. Ultimately, they conducted some 25,000 interviews and pursued “tens of thousands of investigative leads” into assassin Lee Harvey Oswald and other individuals.

Most crucial–and controversial–was the work done by the FBI’s lab investigating ballistics evidence. The Bureau tied the gun to Oswald and identified him early on as the sole gunman. FBI officials later reiterated their confidence in those findings when investigators testified to the Warren Commission.

Some FBI investigations wrap up quickly; others, like the attempt to bring the murderer of civil rights leader Medgar Evers to justice, drag on for decades. A bullet felled Evers on the front doorstep of his Jackson, Mississippi, home in June 1963, but it wasn’t until 1994 that evidence collected by the FBI finally helped convict white supremacist Byron De La Beckwith for the assassination.

The Bureau almost immediately connected the murder weapon to the culprit: De La Beckwith had dropped the firearm after its recoil drove the rifle scope into his eye and it had been located by police. But two all-white juries rejected the testimony offered by FBI agents and other witnesses. As Evers’ widow prodded local prosecutors to reopen the case, the FBI helped locate new witnesses. De La Beckwith was finally convicted in 1994 and died in prison in 2001.

On a November afternoon in 1971, a man who identified himself as “Dan Cooper” bought a one-way ticket on Northwest Orient Flight 305 from Portland, Oregon, to Seattle. Once the plane took off, the quiet-looking man wearing a business suit told a flight attendant he had a bomb in his briefcase, and that he was hijacking the plane. His demand? $200,000 in used notes and four parachutes. In Seattle, he exchanged the plane’s other passengers for the ransom and ordered the pilot to take off again in the direction of Mexico City—and to fly slowly. Then Cooper donned a parachute and jumped out of the plane, somewhere near Nevada, with the cash. Thus began the Bureau’s most famous unsolved case. “Cooper” was never seen again in spite of an extensive search. In 1980, a boy recovered a rotting package of money that had been part of the ransom, but the Bureau’s investigations into 800 or so suspects proved fruitless. The case remains open.

In 1974, the FBI took a lead role in investigating the kidnapping of heiress Patty Hearst, including helping her family try to distribute the “ransom”: $2 million of free food her kidnappers had demanded they provide to the needy. But it took a lot of legwork–and many tips–before informants finally caught up with Hearst, who had decided to throw her lot in with her abductors, a band of domestic terrorists who called themselves the Symbionese Liberation Army. When the FBI finally found Hearst, who had renamed herself “Tania,” they weren’t rescuing a kidnap victim; instead, they charged her with bank robbery and other offenses. Sentenced to seven years, she served two and eventually received a pardon.

The FBI began investigating a series of mysterious bombings in 1980, after one of the homemade devices exploded in the cargo bay of an American Airlines flight and another device was sent to the president of United Airlines. The FBI, teaming up with postal inspectors, quickly noticed design similarities between the two bombs. They also found links to similar attacks throughout the 1980s and into the 1990s; of the 16 incendiary devices placed or sent between 1978 and 1995, many caused severe injuries and three proved deadly. Since the bomber used scrap materials, and left few if any forensic traces, by the mid 1990s all the Bureau had to go on was a rudimentary profile. Only when the agency and the Justice Department greenlit newspaper publication of a 35,000-word manifesto by the so-called Unabomber did a social worker named David Kaczynski alert the FBI to similarities between the screed and the thinking and writing style of his brother Ted. The FBI led the team sent to arrest the Unabomber at a remote shack in Montana, discovering a live device ready to mail under his bed. Kaczynski pled guilty and died in prison.

On the morning of April 19, 1995, a truck exploded outside the Alfred P. Murrah Federal Building in Oklahoma City. The massive blast killed 168 people (including 19 children), injuring hundreds more and causing about a third of the large office building to simply collapse. It was the single worst case of domestic terrorism in American history, and while the FBI helped to identify and locate the bomber, Timothy McVeigh, within two days, it would require a complex investigation to convict him and his co-conspirators. A total of 28,000 interviews provided insight into McVeigh’s motives and movements; the FBI also reviewed some three tons of evidence. McVeigh, convicted of the crime, was executed in 2000.