Luminol reagent, often used in film and television works to reveal bloodstains.

In the past, Luminol needed to be prepared on-site, but now there are ready-made products available.

Luminol has a strong ability to detect bloodstains.

How strong? Bloodstains from several years ago can be revealed if no special treatment has been done.

Even if the blood is diluted 1 million times, it can still be easily detected by Luminol, even in the case of one drop of blood in a bathtub full of water.

Therefore, trying to clean bloodstains with water is basically futile in front of Luminol.

This is also why it is generally not advisable to commit murder at home.

Luminol is a very cheap reagent. 0.1 grams of Luminol, mixed with 5 grams of sodium carbonate and 6 milliliters of hydrogen peroxide, can produce a 100-milliliter bottle of Luminol solution.

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It is also used for spraying to conduct inspections. It doesn't take long to spray a room.

Moreover, DNA technology is now very advanced and highly sensitive. The bloodstains revealed by Luminol can easily soften the bloodstains, and with a swab, DNA can be easily obtained.

Furthermore, ordinary toiletries and cleaning products are unlikely to clean bloodstains to the extent that Luminol cannot detect them.

To interfere with Luminol, an oxidant is needed, the most common being bleach and potassium permanganate. However, they cannot completely interfere with the Luminol reaction, because the luminescence time of hemoglobin and interfering substances is different, and experienced crime scene investigators can easily detect the difference.

As for the hotel bathroom, naturally, these things are not used.

Moreover, the cleaning aunt in the bathroom has never been known for being diligent.

Jiang Yuan took several photos before the Luminol stopped glowing and then said, "Master, you can turn on the lights now."

"Okay." Wu Jun turned on the lights, his face beaming with a smile.

"Why are you so happy?" Jiang Yuan put on gloves and a mask, and then took out a cotton swab, operating meticulously.

If nothing unexpected happens, these bloodstains will be the key evidence in this case.

There is no room in Bai Yuequn's entire set of lies for the bloodstains of Yuan Yutang and her boyfriend.

Wu Jun watched Jiang Yuan swabbing the cotton swab with a relaxed expression and said, "Even if they are as cunning as ghosts, they still have to drink my washing water."

"We haven't done the DNA test yet," Jiang Yuan reminded.

Wu Jun chuckled and made a gesture with his hand, saying, "Unless both of them have hemorrhoids that have burst, this place is definitely where Bai Yuequn cleaned up the bloodstains."

Jiang Yuan nodded and made a slight correction, "Unless in recent years, someone's hemorrhoids have burst in the bathroom, this place is basically the scene where Bai Yuequn cleaned up the bloodstains."

"Let's be more rigorous, but... where are the bloodstained clothes and murder weapon?" Wu Jun furrowed his brow slightly.

In the city, bloodstained clothes and murder weapons are difficult to dispose of. Jiang Yuan also had no idea for a moment and said, "Let's first break through Bai Yuequn's alibi."

"That's right. If Xu Yi doesn't speak, we can scare him with the death penalty, and he will definitely talk," Wu Jun said with insight.

During the interrogation stage, criminal suspects cannot see a lawyer and can only listen to whatever the police say. Therefore, if they don't study well, they will be exploited due to lack of information after committing murder or being an accomplice to murder.

Bai Yuequn's fencing teammate looks like an easy target.

...

In the evening.

Lei Xin made a careful plan and was ready to interrogate Xu Yi personally.

Lei Xin started his career in pre-trial investigation. In fact, when there was a pre-trial department, the police officers who could enter the pre-trial department were all highly competent. His teeth, stained yellow from smoking, were also a testament to his experience.

After carefully reviewing the DNA report again, Lei Xin walked into the interrogation room with high spirits.

Xu Yi was tall and thin. After his hands and feet were locked to the interrogation chair, he looked like a giraffe playing with bondage, with only his head stretched out.

"Do you know what we want to ask?" Lei Xin had interrogated Xu Yi briefly before, and this time he sat across from him with a smile, placing a thick stack of files on the table.

That pile of files looked like a lot of evidence and testimony, which also caught Xu Yi's attention, and he couldn't help but look over and speculate in his mind.

After a while, Xu Yi turned his gaze back and said, "I know you want me to confess."

"I want to save your life, I don't want to see you become a scapegoat," Lei Xin decided to use a soft approach, first taking out several photos of Bai Yuequn scouting the area and said, "These are photos of Bai Yuequn scouting that we captured."

The video surveillance team found a lot of videos, and Lei Xin showed them to him one by one.

After looking at them, Xu Yi turned his head and said, "There's no need to show them. That's the movie theater closest to the bar street. We just went to watch a movie, that's all. What's the big deal?"

"Your explanation has some merit," Lei Xin seized the opportunity to praise Xu Yi and then showed the damaged surveillance footage and the time of the second screening room.

Then he showed the photos of Bai Yuequn entering and leaving the cinema around the same time.

After seeing this, Xu Yi simply closed his eyes and said, "If you can't find the real killer, just arrest us directly. There's no need for all this nonsense."

Looking at his expression, Lei Xin silently took out his trump card and said, "I also have a DNA report from the hotel room where you stayed that night. How do you explain this?"

Xu Yi was taken aback, "What do you mean?"

"There are bloodstains from two deceased individuals in your hotel room, quite a few of them," Lei Xin said calmly, "It should be the blood that Bai Yuequn didn't clean up at the scene."

After a moment of hesitation, Xu Yi said, "You're lying to me."

"Suppose I am lying to you. If I go to the bathroom of the hotel where you stayed to find bloodstains, do you think I can't find the bloodstains of the two deceased individuals?" Lei Xin held the DNA report in his hand and didn't give it to Xu Yi.

Xu Yi couldn't hold on any longer.

"Do you really want to spend the rest of your life in prison like Bai Yuequn?" Lei Xin began to use a sympathetic approach.Xu Yi's expression shifted slightly, and after a moment, he said, "There's still work to be done."

"What?"

"Bai Yuequn promised me, to keep my mouth shut, and in return, he'd find me another job. If we were to be convicted of a criminal offense, it would be hard to find work." Xu Yi's voice was very soft.

Lei Xin was overjoyed; as long as the conversation started, the rest would be easy to inquire about.

Lei Xin asked, "Let me ask you again, during the movie screening that day, were you with Bai Yuequn in Cinema 2 watching the movie, and did either of you leave at any point?"

Xu Yi replied, "I don't know."

Lei Xin could hardly contain himself; if he were allowed to devour someone, he would grind Xu Yi to a pulp in his mouth.

"I really don't know," Xu Yi continued. "As soon as I entered the screening room, I felt a bit tired, so I fell asleep. Whether Bai Yuequn left or not, I have no idea."

This statement couldn't incriminate Bai Yuequn, but it was enough to shatter his alibi.

Not just Lei Xin, but everyone monitoring the situation couldn't help but chuckle.

Lei Xin pressed on, "On the way from the cinema to the hotel, did you notice Bai Yuequn discarding anything?"

Xu Yi answered, "No."

"What about any smells? Did you notice any odors?"

"I was wearing a mask at the time, an N95, so I didn't smell anything."