Which is the first item listed under postmortem intervals (PMI)?

• A. Rigor Mortis
• B. Livor Mortis
• C. Algor Mortis
• D. Entomology

Answer: (A)

Rigor mortis is the first item listed because it represents the earliest clear physical change after death that helps estimate time since death. After death, lack of ATP causes muscles to stiffen and become rigid. This stiffening begins in smaller muscle groups (like the face and jaw) and usually progresses to involve the rest of the body, typically starting around 2–6 hours postmortem and reaching full rigidity by about 12 hours, then gradually dissipating over the next day or two. Because its onset is relatively time-bound and observable, it’s commonly placed first in PMI checklists to anchor an early time frame.

Algor mortis (body cooling) is also an early change but is highly influenced by environment, clothing, and body mass, making it less precise for narrow PMI windows. Livor mortis (blood settling) appears within hours and becomes fixed later than rigor mortis in many cases. Entomology involves insects and is generally used to refine PMI estimates later in decomposition.