Chapter 155: Footprints

The dust fixative purchased by the Ningtai County Bureau was made from alcohol solvent with rosin added.

This is a very old-fashioned fixative, with slightly lower transparency and a longer drying and fixation time.

Jiang Yuan sprayed a row of fixative on the staircase; by the time he finished spraying the rear sections, the footprints ahead had only just begun to appear.

At this point, ordinary crime scene investigators or trace examiners would typically dust for prints. Jiang Yuan didn't need this step—he simply studied the footprints, savoring their raw essence.

But it was only a cursory glance.

Most of the footprints were probably left by security guards.

The security guards at Wanghe Building all wore leather shoes and small ties—useless, but they looked reasonably formal.

Jiang Yuan continued spraying the fixative, placing transparent forensic footplates on areas without footprints and advancing step by step until the entire staircase from the 27th to the 29th floor had been treated.

Then, Jiang Yuan set up the specially transported crime scene footprint light source.

"Crime scene footprint light source" sounds like a highly professional device, but it's just a high-power LED lamp, fitted with a housing to provide a relatively reasonable height and rotation angle.

Of course, lithium batteries were essential—they ensured portability and sufficient power for outdoor use, while also keeping costs and profits in check.

The footprint light source purchased by Ningtai County had a power output of 100W and a color temperature of 6000K, closely simulating natural daylight. When shone on the ground, the footprints freshly coated with fixative appeared with startling clarity.

Finding footprints, fingerprints, and trace evidence all rely on essentially the same tools.

The equipment is indeed useful and convenient, but before today, Jiang Yuan had never bothered to bring it along.

For instance, at the fall scene just meters away, Jiang Yuan had used natural light during the day and a portable small light at night to find numerous trace evidences—he hadn't felt the need for such a large light source.

But given the current situation—if a criminal really returned to the crime scene—then naturally, one used whatever equipment was available.

Ordinary homicide cases—or rather, the kind of homicide cases regular police officers typically encounter—are almost always committed by novice criminals; seasoned repeat offenders are so rare that most officers never encounter one in their entire careers.

But if a criminal truly returned to the crime scene, one certainly couldn't treat him as a novice.

Anyone who reached this level could reasonably be described as calm and composed.

And calmness at a murder scene often meant few traces were left behind.

The footprint light's illumination spanned about one meter wide and extended deeply; Jiang Yuan swept it across the area in sections.

Wang Zhong, who had come with him, watched Jiang Yuan move the light source twice, then immediately ran over and volunteered to handle moving it.

Jiang Yuan thanked him, stepped onto a transparent footplate, leaned against his waist, rested, and observed the numerous footprints before him.

As for calmness, how could police ever lose to criminals?

In terms of technique, the police system had never won.

Being technologically ahead was something police rarely enjoyed.

Most of the time, what police had was "calmness and composure," the slow grind of persistence and ironclad footwork, organizational discipline and execution power.

Jiang Yuan suppressed his urge to make a quick judgment and examined each footprint one by one.

Security guards' footprints were the most numerous, but their priority was the lowest.

Some of the security guards' footprints stepped directly over earlier ones, clearly indicating the patrol direction.

Jiang Yuan was glad he'd notified the team leader; otherwise, if he'd come alone, the security guards would have trampled the scene—and organizing their subsequent patrols would have been extremely difficult.

If the murderer was a security guard…

Jiang Yuan shook his head and first focused on footprints outside the security guards' leather shoes.

There were three sets of footprints: two faint ones and one deep one.

The two faint sets were about 30 years old, corresponding exactly to a downward walking path.

The deep set came upward, circled a few steps in place, then exited outward…

In fact, not just Jiang Yuan—several others present had also noticed this newly visible set of footprints.

In ordinary cases, footprints and fingerprints are typically collected by regular detectives or detectives working with crime scene examiners—meaning, collecting footprints and fingerprints alike are basic skills for detectives.

Moreover, at ordinary crime scenes, detectives selectively collect fingerprints and footprints; otherwise, collecting every single print and footprint in a room would overwhelm even the most experienced technicians.

Only at homicide scenes could one afford such luxury.

Now, facing this newly visible footprint beneath them, everyone recognized the problem.

This was the most likely suspect's footprint seen so far.

The direction of the footprint also spoke volumes.

This person entered from the 27th floor, lingered on the 28th floor, then opened the 28th-floor fire door and exited.

When checking the fire staircase on the 27th floor, one could see he had entered through the 27th-floor fire door.

He headed straight for the 28th floor—if he wasn't the murderer, it was too much of a coincidence.

"Door handle," Wang Zhong whispered to Jiang Yuan, urging him to look for fingerprints first.

Jiang Yuan nodded. There were multiple footprints on the ground; he could collect them later.

Jiang Yuan stepped onto the footplate and approached the fire door, shining the light on the handle.

At a glance, it was a clean, highly reflective stainless-steel handle.

"Wiped clean," Jiang Yuan murmured.

Wang Zhong blinked: "So thorough?"

Jiang Yuan nodded.

Though he desperately wanted to find evidence, he had to admit that finding fingerprint evidence was becoming increasingly difficult.

Thoughtful criminals took various measures to avoid leaving fingerprints: the simplest was wearing gloves; some wiped touched surfaces; others even burned their fingertips.

Wang Zhong looked slightly disappointed—Jiang Yuan could accept that.

He stared blankly at the footprints on the ground.

If he'd been the only one present at the scene, and the man had walked out wearing gloves, pulling his hat brim low, and donning a mask…

"Can footprints reveal age and height?" Huang Qiangmin called from the periphery.

Jiang Yuan quickly snapped back, studied the footprints again, and said: "Male, age 45 to 49, medium build, height around 170 cm…"

Just an ordinary person.

This was also the most troublesome aspect of footprint analysis—it revealed too few distinctive features.

Huang Qiangmin, following Jiang Yuan's description, first sent out a mass text message, then, seeing the others' low spirits, encouraged them: "People aged 45 to 49 shouldn't be numerous in this building. Start looking."

Jiang Yuan gave a slight nod. Dust footprints provided less information than blood footprints, but still, it was progress.

As Huang Qiangmin said, the age range of 45 to 49 had already narrowed the field considerably.

"Is the age accurate? Should we widen it a bit?" Wu Junhao, who had been standing nearby, finally spoke up.

"I gave the age in full years. If you're worried, extend it by two years," Jiang Yuan said, considering regional age conventions and accommodating Wu Junhao's suggestion by widening the range by two years.

But in terms of accuracy, judging age from footprints was indeed less precise than judging height or weight.

In fact, the simplest method to judge age from footprints was something any layperson could easily learn.

Divide the footprint vertically into four equal sections: the innermost line corresponds to ages 18–23, the second line to 24–29, the center line to 30, the third line to 31–39, and the outermost line to 40–49.

Jiang Yuan naturally combined other information in his judgment, but even half of this method was sufficient.

"Multispectral," Jiang Yuan called out again.

An officer immediately ran out and returned with a multispectral light device.

This tool also assisted in locating traces.

It was especially effective for finding trace evidence.

Many substances emitted fluorescence under specific wavelengths.

Jiang Yuan adjusted the multispectral device to 450 nanometers and began scanning near the fire door.

Perhaps some fibers had been left behind.

But none were found.