The method of Green and Wright for estimating the time of death uses rectal and environmental temperatures. It assumes that a double exponential mode adequately describes how the body cools.
gradient G =
= ((rectal temperature in °C at time 2) - (rectal temperature in °C at time 1)) / (time interval in hours between time 1 and time 2)
where:
• The original equation shows temperature at time 1 minus temperature at time 2, but states that G is always negative, since the latter temperature is always greater than the former.
gradient A =
= (((rectal temperature in °C at time 1) + (rectal temperature in °C at time 2)) / 2) - (average environmental temperature in °C)
reduced theta =
= ((rectal temperature at the time of death) - (((rectal temperature in °C at time 1) + (rectal temperature in °C at time 2)) / 2)) / ((rectal temperature in °C at time of death) - (average environmental temperature in °C))
where:
• The rectal temperature at the time of death is assumed to be 37°C.
Estimation of F
For reduced theta between 0 and 0.639, the rise in F is linear, and is approximated by the equation derived in JMP:
F =
= (1.8826 * (reduced theta)) - 0.026636
For reduced theta from 0.639 to 0.96, the rise in F is exponential, and can be approximated by the equation derived in JMP.
F =
= (317.62648 * ((reduced theta)^4)) - (926.6809 * ((reduced theta)^3)) + (1014.8223 * ((reduced theta)^2)) - (491.3695 * (reduced theta)) + 89.622192
Calculation of Time Since Death
time since death in hours =
= (-F) * ((gradient A) / (gradient G))
Limitations:
• The method assumes that the rectal temperature at the time of death was normal, which may or may not be an accurate assumption.
• The method assumes that the environmental temperature remains relatively constant over the time since death.
