What is most likely to determine the length of time a corpse has been dead

The amount of skin left on the corpse.
Hope this helps! :D

INTRODUCTION

Time is one of the most important factors of consideration in a murder case. It may very well convict a murderer, break an alibi, or eliminate a suspect. If the circumstances surrounding death indicate the possibility of homicide, then both the body and immediate surrounding area become crucial in estimating time of death. Estimating the time of death, especially in cases where there are no witnesses, is critical to the investigation.

Time may focus attention on various suspects. For example, the deceased may have had an appointment with someone at a specific time. Or, in cases of "exclusive opportunity" (where only certain persons are present during a specific time, e.g., husband and wife during the evening) if one of those persons is found in nightclothes the following afternoon dead from a beating, and the estimation of time of death places the incident in the range of 3 A.M. to 6 A.M., the spouse is sure to be the suspect.

A definite time of death can corroborate or disprove a suspect's alibi. Those circumstances are extremely rare e.g. a bullet hitting and stopping a watch or an eyewitness who was present when death occurred and noted the time.

In civil matters, time may be the factor that determines whether or not an insurance policy was in effect or was void. Most insurance companies include "suicide clauses" in their policies whereby they are released from contract to pay if the insured commits suicide within a specific time, usually within one year after becoming insured. Furthermore, in probating a will, it can be crucial to learn whether the husband or wife died first, since the estate usually goes to the one who expired last.

Throughout the years, forensic scientists and pathologists have searched for a definitive method of determining time of death, yet at present there is no single reliable method. Moreover, it is impossible to fix the exact time of death; hence, we refer to an estimated time. Based on an appreciation of a large number of variables, an experienced pathologist can arrive at a reasonable estimation of time of death; usually placing it within a range of hours. The process is subject to error, especially if some crucial piece of information is omitted. It should be noted, however, that this estimation certainly represents more than just an educated guess. It is a scientifically derived opinion based on a totality of specific factors distinctive to each particular case compared with ordinary time factors attributed to the pathological changes that occur in a human body.