K4 was cracked by Ian James Colmer, who submitted the partial solution to JS. confirming the strand he extracted.
Basically he laid the ciphertext of K4 across the edges of a tabula recta, then entered the ciphertext of K1-K3 as the body of the tabula, and then used a series of abscissas to chart the locations of the plaintext to extract……finding the solution from a final complication shown in detail step by step.
Seeing the Green Blob on the Red Rock being from Vermont, and the Tabula taking the shape of the Masonic Temple of Burlington as the Blueprint for the cipher, I later added to it, to identify the building the tableau was shaped to mimic. The Abscissa in the corner of K4 also said VT but the whole puzzle had to be adjusted to deliver the configuration for the flips to Layer Two…. identifying one suspect in their tell all reveal.
Explained in detail here: