"Paranormal Death or Ritualistic Murder"?

[Mudhammam]

which are plausible substances that would break down or become undetectable after a body has been decomposing for 19 days?

That's a really good point. Could a toxicology report be reliable after three weeks of decomposition?

And to Rebecca's question, did they find her clothes somewhere?

The most striking aspect to me, aside from her odd behavior in the elevator (and the elevator's behavior) and the mystery of how she ended up in the tank, is the name of the tuberculosis test, Lam Elisa, and the outbreak of the illness on skid row shortly after her disappearance. This goes to show how remarkable coincidences can seem, yet, no doubt, that's all it was.