In the spring of 1963, a Portland, Oregon garage band called the Kingsman went into a local studio and recorded their infamous single. The lead singer, Jack Ely, had braces on his teeth, and his microphone was too far away, which led to his especially mumbled delivery on the band’s version of “Louie Louie,” according to The New Yorker. The song soon became a hit for the band and sparked the FBI probe. “Kids … would hear these versions of the song, and they would pass around these written notes of what they thought were the lyrics,” documentary filmmaker Eric Predoehl told NPR in 2015.

The FBI and Justice Department also received concerned letters from Florida, Michigan, and elsewhere. Eventually, six FBI field offices got involved, with agents interviewing record executives and the song’s composer, Richard Berry — but not singer Jack Ely, according to “The Mind of the Censor and the Eye of the Beholder: The First Amendment and the Censor’s Dilemma.” The FBI scientists slowed the recording down and sped it up, “but it was indecipherable at any speed,” Predoehl told NPR.