Step 1: Understanding the Question:
We must find the one item that is not really an obligation of a doctor performing a medico legal post mortem examination, while the other three are genuine duties.
Step 2: Key Formula or Approach:
Think about what a post mortem report is meant to do: it is a careful, complete, and documented medical record that gets passed through official channels for legal use. Match each option against that purpose.
Step 3: Detailed Explanation:
A meticulous and complete examination is required because the post mortem is often the only chance to record the true cause and circumstances of death, so nothing should be rushed or skipped.
Recording both positive findings and important negative findings is required because absence of an expected sign can be just as telling as its presence, and a complete report needs both.
Preserving viscera and sending them for toxicology in suspected poisoning is required because chemical evidence in the body can be lost quickly, and proper preservation lets the analysis confirm or rule out poison later.
Keeping the police informed about the findings, however, is not listed as a standing duty of the doctor. The proper channel for the findings is the official post mortem report sent to the requesting authority, such as the investigating officer or magistrate, not an ongoing informal update to the police. The doctor is also expected to maintain confidentiality of medical findings outside the formal report.
Step 4: Final Answer:
The exception is keeping the police informed about the findings, since a doctor's real duty is a thorough report through the official channel, not routine informal reporting to the police.