Death Occurs — Circulation Stops
Heart stops, and gravity begins pulling blood downward immediately.
- 0.0 h: Time of death (reference point)
- Relaxed: Muscle tone (primary flaccidity)
- 0 mmHg: Blood pressure (no circulation)
- ~0.8°C/h: Core temp drop (algor mortis begins)
Primary flaccidity
All muscles instantly lose tone and go completely limp.
Gravity takes over
Unpumped blood starts sinking toward the lowest vessels.
Body position at the moment of death shapes the entire pooling pattern.
The forensic clock starts
Investigators treat this moment as time zero for estimates.
Livor Mortis Onset — Blood Pools by Gravity
Blood sinks into capillaries along the lowest body surfaces.
- 30 min: First visible mottling (faint pink-purple)
- ~6-8 h: Fully blanchable until (pressure clears color)
- Purple-red: Typical color (deoxygenated blood)
- Yes: Repositioning shifts it (not yet fixed)
Dependent pooling
Skin over the lowest points darkens visibly with settled blood.
Still movable
Pressing the skin still blanches the color away completely.
Moving the body now still fully redistributes the pooling pattern.
Diagnostic value
Pattern location hints strongly at body position after death.
Rigor Mortis Onset — Small Muscles Stiffen First
ATP depletion locks actin and myosin filaments together.
- Jaw, fingers: First muscles affected (small muscle mass)
- 2-6 h: Onset window (variable with temperature)
- ATP depletion: Cause (actin-myosin cross-bridges lock)
- Heat, exertion: Accelerated by (faster ATP loss)
Why small muscles first
Less tissue mass means faster local ATP exhaustion.
Cross-bridge locking
Actin and myosin filaments bind and simply cannot release.
Rigor spreads head-to-toe in a fairly predictable order, called Nysten's rule.
Temperature dependence
Warm settings speed onset; cold settings delay it noticeably.
Rigor Mortis Peak — Full-Body Rigidity
Every major joint locks as large muscles finish stiffening.
- ~12 h: Peak onset (full rigidity)
- 12-24 h: Plateau duration (sustained stiffness)
- All major joints: Joints affected (jaw to ankles)
- Fixed: Livor mortis by now (no longer blanches)
Whole-body lock
Large muscle groups finish stiffening by roughly twelve hours.
Livor fixation overlaps
Blood pooling has now set permanently into place.
A mismatch between position and pooling pattern signals the body was moved.
Estimating time since death
Combined rigor and livor staging narrows the estimate window.
Rigor Mortis Resolution — Decomposition Begins
Enzymatic tissue breakdown releases the stiffened muscle fibers.
- 24-36 h: Resolution window (stiffness fades)
- Autolysis: Cause (cellular enzymes break down tissue)
- Flaccid again: Final muscle state (secondary flaccidity)
- Permanently fixed: Livor pattern (unaffected by resolution)
Secondary flaccidity
Muscles relax again as structural proteins decompose.
Decomposition accelerates
Bacterial and enzymatic activity now dominate the timeline.
Past 36 hours, rigor mortis no longer reliably aids time-of-death estimates.
Limits of the method
Temperature, body size, and clothing all shift these windows.