The truth of the matter is that no one knows what happened to Günther Stoll before his death in October 1984 or what his cryptic message — YOGTZE — meant, but that doesn’t mean that there’s a shortage of theories floating around (via Historic Mysteries).

Given that YOGTZE isn’t a word in any known language, some have speculated that the “G” is a “6,” while the “O” could be a “0” and the “Z” a mistaken “2.” This would be Y06T2E, which some have argued could be a license plate, meaning Stoll was leaving a clue as to who may have wanted him dead and who was involved in his death. Of course, seeing as the word was written hours before his death, that seems unlikely. That same number is also the call sign for a Romanian radio station, but there’s nothing else to this connection apart from the coincidence.

Others have pointed out how YOGTZE is an anagram of “zygote,” one of the earliest stages of human development, and have speculated that perhaps the word somehow ties back to Stoll’s work if he had worked on a project related to food — or even genetic — modification.