Well, first off, they aren't dodecahedrons, which are regular solids made of 12 equal pentagonal faces. They're
cuboctahedrons, irregular solids with 8 triangular faces and 6 square faces (14 in all, so they're a type of tetradecahedron).
As for the rest, though Rojan says they're the flesh distilled into that form, they're clearly much lighter than a human body. Perhaps Bixby and Fontana were thinking of some kind of dehydration process like in the 1966
Batman movie, where dehydrating people reduced them to a few ounces of powder. But then where does the water go?
I'd imagine the solids are really more some kind of storage medium containing the person's molecular pattern. That would make them analogous to transporter buffers, in a sense. If they store that pattern the same way a transporter does, then there's probably some redundancy and robustness against pattern loss, since we've seen people able to be restored intact from transporters even when their patterns suffered considerable degradation. I suspect transporters use quantum error correction, which involves spreading information redundantly among multiple entangled qubits (quantum bits), so that the complete information can be recovered as long as enough qubits survive. The cuboctahedrons might work similarly.
Alternatively, they might have holographic storage -- not in the vernacular sense of a "hologram" as a volumetric image, but in the literal sense of a storage medium where information about the whole is encoded in each part, so even if parts are damaged or lost, the complete information is still recoverable.
Even if we assume that the solids are constituted from the victims' own biomass somehow, I doubt there's a one-to-one correspondence of volume to volume, so that there's a piece to break off that would cause someone to reform without a hand, say. Let's say the pattern information is stored throughout as I suggest, but damage could cause the person to lose part of their mass. Then they'd probably be reconstituted with a loss of weight, say, maybe with some mineral deficiency. But I'm skeptical that they're literally constituted from biomass. Then they'd presumably be mostly carbon, in which case they'd probably look like lumps of coal. So I'm sticking with my storage-medium idea.