Pro forma? You make absolutely no sense. No sense at all. Are you saying that a coroner has no authority to determine the manner of death? There have been murder cases brought to trial with convictions with no cause of death proven, but with a determination that the manner of death was homicide. If a corpse is too decomposed to determine whether or not death was caused by strangulation, poison, or suffocation, an ME or a coroner can still determine that a homicide occurred.
From Contra Costa County's coroner's website:
"The Coroners primary duty is to determine the cause, manner and mode of death as a result of homicide, suicide, accidental or unexplained deaths. The determination of death is reached through examination of evidence, scene investigation, review of medical records, witness and doctor interviews as well as autopsies and/or Coroner Inquests."
A coroner makes determinations that are legally defensible, and are used in court. But it seems that that doesn't matter to you.
In the absence of a corpse, how are we to know that a murder has occurred? There could be a witness to a murder and the victim is missing, and a trail of supporting forensic evidence, for example.
But in this case the body gives no evidence that the cause of death was homicide, so we must to go other evidence ... and that evidence is lacking, as I pointed out. No eyewitnesses, no evidence of a murder weapon having existed much less one that links the victim to a suspect, no crime scene, no known time or place of death, no forensic evidence that isn't compatible with common transference.
It's counter-intuitive that Scott Peterson -- who was so clumsy in his lies that even the clueless Amber Frey figured it out -- committed an otherwise perfect crime.