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To Shen Yuan's surprise, there were no large scale movements of any insects on the body, as the lower legs clearly had the destructive activity of a white-bellied skin pouch.

On the upper surface of the corpse, and at the edge of the clothing, were the empty pupa shells of the two common flies, the large head and the red.

The formation of an empty pupa shell usually takes at least 17 days.

However, for a corpse exposed to the open air for 17 days, the pitifully small number of insects is unusual.

So what is the reason for this anomaly?

The smart Shen Yuan looked at the half of the rope hanging from the tree, then looked at the surrounding terrain, and quickly made his judgement and analysis.

It was impossible to judge whether she had been hanged from a tree after her death or from a tree after her death.

But it was certain that the rotting corpse must still be hanging from the tree.

When the body was suspended, the flies came to lay eggs on it.

As the flies hatched, they turned into a swarm of maggots that began to devour the corpses.

Due to the gravitational force, maggots constantly fell to the ground.

This continued to reduce the number of maggots on the corpses.

The maggots that fell to the ground would die if they couldn't find food.

As the body decays, fluid and bits of flesh fall from the body to the ground.

A very small number of maggots had completed their development at the place where the maggots fell.

This is why a few chrysalis shells can be seen.

This effect is accelerated by the flow of wind and air.

Obviously, it would be wrong to infer the time of death from the formation of the chrysalis shell over time, since the period after the death of the chrysalis was still unknown.

Undoubtedly, this raises a new question for forensic entomology about the time of death.

After returning to Qinglong Town, Shenyuan has checked a lot of information on the internet and found that the surface of the chrysalis shell contains different amount of hydrocarbon when eluted by organic solvents.

This hydrocarbon is usually derived from the components of the chrysalis shell and is made up of hydrocarbons that are continuously degraded.

As the time of exposure of the pupa shell, the lower the organic matter content in the pupa shell, the lower the hydrocarbon content naturally.

As the time interval between pupa death lengthens, the content of some volatile hydrocarbons will decrease regularly in pupa shell.

Just as we pour a barrel of gasoline with a mixture of molecular weight and size onto the ground, as time goes by, the lighter gasoline will first evaporate into the air, that is, the proportion of light oil remaining on the surface will gradually decrease with time, while the proportion of heavy oil on the surface will increase with time.

The amount of gasoline on the ground will gradually decrease due to the constant evaporation into the air.

Of course, the law of volatility is affected by the ambient temperature, even by the wind.

You can predict when the gasoline will be on the ground by the proportion of light oil in the base area.

According to a similar rule, you can calculate how long it has been since the chrysalis shell was formed, based on the ratio of volatile hydrocarbons in the chrysalis shell, and you know when the maggots have become pupae.

In this way, the volatile hydrocarbons were extracted from the epidermis of necrotic flies and their percentages were analyzed. The time interval after pupa death and the time of pupa development during pupa period could be used to determine the time of corpse death.

Shen Yuan sent the pupa shell back to the Central South University Inspection Center and analyzed the surface content of the pupa shell by gas chromatography.

In order to truly explain the time of death, Shen Yuan had also placed a dead pig on the mountain, and analyzed the pupa shell after pupation, and grasped the volatile hydrocarbon content of the pupa shell every day. With a certain data model, as long as the data model was established and compared with the hydrocarbon content of the pupa shell collected on the spot, the number of days of pupa time could be calculated.

Shen Yuan told the technician his test method.

Two days later, the results of the test were sent by fax, indicating that the corpse had been dead for at least two months.

Shen Yuan immediately reported his deduction to the Lai City Public Security Bureau and asked them to investigate whether Zhou Zhiqiang had ever been to Lai City two months ago, including the time he had been in Lai City and the footprints left behind by his activities.

Subsequently, a DNA test by the medical examiner confirmed that the deceased was Zhou Zhiqiang.

It was hard to tell whether it was murder or suicide.