The crime was an act of racial hatred on the church, which hosted key civil rights meetings and had been the target of many bomb threats. The FBI launched an investigation immediately and continued throughout September and October as agents infiltrated the Ku Klux Klan and other local anti-black groups.
By 1965 the FBI had serious suspects, including KKK members Robert E. Chambliss, Bobby Frank Cherry, Herman Frank Cash and Thomas E. Blanton, Jr. But locals were hesitant to talk and there was little physical evidence.
Ultimately, Chambliss's conviction and life sentence in 1977 led to the cooperation of previously reluctant witnesses, and after the case re-opened in the mid-1990s, Blanton and Cherry were convicted and sentenced to life in prison in 2000. Cash had died in 1994.
Wall Street Bombing
One of the first acts of terrorism on U.S. soil still remains a mystery.
The flood of Wall Street lunch-goers didn't notice a nondescript man on a horse-drawn cart outside the U.S. Assay Office on Sept. 16, 1920. After the man quickly disappeared into the crowd, the cart exploded, killing more than 30 people and injuring near 300 as metal fragments rained from the sky.
Speculations of conspiracy and terrorism abounded, but crews cleaned the damage overnight (not realizing they were destroying crucial evidence), leaving almost no clues behind.
The best tip came prior to the explosion. A letter carrier found four crudely spelled and printed flyers in the area from a group demanding the release of political prisoners. The group, called the "American Anarchist Fighters," resembled the Italian Anarchists that used similar flyers in two prior bombing campaigns.
The FBI originally suspected followers of Italian Anarchist Luigi Galleani, but the case couldn't be proved and promising trails became dead ends.
The case remains unsolved.
Hollow Nickel, Hidden Agent
A Brooklyn newspaper boy dropped a nickel in 1953 and the coin split in half, revealing a miniature photograph with a series of numbers too small to see. As he picked it up, he was unaware that he held the nation's security in his hands.
Deemed evidence of counterintelligence, the nickel made its way to the FBI. The bureau began questioning people who handled the nickel and novelty store owners who might sell similar products, but they got no leads. FBI Lab scientists in Washington, however, realized the coin's type-print came from a foreign typewriter, and that the photograph was a coded message, but they couldn't crack it.
Four years later, when Russian spy Reino Hayhanen defected to the U.S., he led agents to a "dead drop hiding place" where the FBI found a hollowed-out bolt with a typewritten message inside.
He shared similar hollowed-out items, including a coin, and the connection was made. Hayhanen aided in cracking the code, which put them on the trail of Soviet spy Colonel Rudolf Abel, who Hayhanen believed to be the nickel's owner.
Abel was convicted and sentenced to jail in 1957, but he evaded his prison time as he was exchanged for an American pilot, Francis Gary Powers, who was shot down over the USSR.
The so-called "Freedom Summer" marked a massive three-month initiative to register southern African-Americans to vote as a counterattack to the Ku Klux Klan's campaign of fear and intimidation.