Guessed Wrong

Xu Mo's thoughts suddenly became clear.

He recalled the two rooftops he had visited at the scene today.

Although the two rooftops were different in size, their structures were quite similar.

To access the rooftop, taking the elevator wouldn't work; one needed to climb the stairs leading to the roof. At the stairway entrance on the rooftop, there was typically a square-shaped small house, mainly serving as a shelter from wind and rain.

If the killer had hidden on top of that small house, wouldn't they have been able to avoid the police's line of sight?

When they went to investigate the scene today and didn't see anyone, it might have been because the killer was hiding on the roof!

The more Xu Mo thought about it, the more plausible it seemed.

He immediately took out his phone, snapped a photo of the game screen on Zhou Qiaoqiao's phone, and sent it to Han Fei.

Meanwhile...

At the police station.

Han Fei, who was working overtime investigating the case, heard his phone ping.

Picking up his phone and glancing at it, Han Fei found that it was a picture message from Xu Mo.

He unlocked his screen and opened their WeChat conversation.

Why would Xu Mo send me a game screenshot? Is he asking me to play games? I don't even play games... Han Fei thought.

Just as he was about to message Xu Mo saying he didn't play games, he suddenly realized that this game screenshot might not be an invitation to play, but rather had a different meaning.

Because in the game screen Xu Mo sent, there were four players lying prone on a rooftop!

Rooftop, prone players...

Han Fei felt he might understand Xu Mo's meaning, and his eyes immediately lit up.

A second later, Xu Mo, who had just sent him the photo, followed up with another message.

"I think I know how the killer committed the crime. Wang Dachuan's previous guess might have been right."

Han Fei immediately replied: "You mean after killing the victim, the killer hid on top of the rooftop stairway house, which is why we didn't see him when we went up there, right?"

"Exactly."

Instead of continuing to type, Han Fei directly called Xu Mo.

Once Xu Mo answered, Han Fei spoke.

"This theory is definitely possible. From where we were standing, we couldn't see the roof of the stairway house, so even if someone was up there, we wouldn't have known."

"I only thought of this possibility after seeing this game screen," Xu Mo said. "This might be the only way the killer could 'avoid' the surveillance cameras."

Hiding on the rooftop well in advance, waiting for the victim to come up, then pushing them off when they weren't expecting it, and afterward hiding for a while before leaving the roof - while this method wouldn't completely avoid surveillance, it would work as long as they weren't discovered by the police!

After all, when police investigate surveillance footage, they typically only look at footage from a few hours before and after the incident, rarely going back further because it might be pointless and would waste time.

As long as one had enough patience to stay crouched on top of the stairway house for ten hours or even longer, there was a high probability that the police wouldn't trace it back to them.

The killer in this case might have taken advantage of exactly this point.

Of course, this method had major flaws - if the police were to check surveillance footage from much earlier, the killer would be caught.

Simply put, this method was a gamble - betting that the police wouldn't check footage from too far back.

Win the bet and you could get away with it, but lose and you're in trouble... straight to prison you go!

"Since I'm still at the station, I'll review the surveillance footage we copied from the building again... though I only have the footage from before the incident, and only about an hour after - the copied footage only goes up until we left the building," Han Fei said while retrieving the surveillance footage from all three cases.

This time, instead of only looking at footage from a few hours before the victims' deaths, he expanded his search to include the previous forty-eight hours, playing it at increased speed.

Han Fei believed that no matter how much endurance the killer had, they couldn't possibly have stayed prone on the roof for forty-eight straight hours.

Twenty-four hours would be the limit realistically.

But to be thorough, he chose to start checking from forty-eight hours before the incident.

If the killer's method was as Xu Mo suspected, checking the forty-eight-hour period would surely yield results.

"Having just the pre-incident footage is enough. I'll hack into the Guojin Building's surveillance system and take a look too. With two people checking, we'll have a better chance of catching anything we might miss," Xu Mo said.

The footage Han Fei had from the Guojin Building only extended to about an hour after the incident, as that's when they had copied it.

But that was sufficient.

According to Xu Mo's theory, for the killer to fool the police, they would have had to go up to the roof long before the incident and hide.

Only then would there be a chance that the police might overlook someone who had gone up to the roof so early, since when checking surveillance footage, police typically only look at a few hours' worth, not wanting to waste time checking too far back.

If they could find someone who went up to the roof long before the incident and never came down, that person had to be the killer!

At this moment, Zhou Qiaoqiao walked out of the kitchen carrying a bowl of soup.

"Here, it's still hot. This soup has been simmering for a long time. You've been busy all day, have some soup to replenish your energy!"

"Thanks, just put it on the table. I'll drink it in a bit," Xu Mo said with a smile, handing back Zhou Qiaoqiao's phone. "Here's your phone."

Zhou Qiaoqiao took the phone, returning his smile.

"No need to be so polite, you've helped us too. If it weren't for you taking us in, the four of us wouldn't even be able to sleep soundly at night, what with all those ghost stories... too scary."

...

Xu Mo went to his room and opened his computer.

In no time at all, he had hacked into the Guojin Building's surveillance system.

He was also going to check the footage.

Having another person check provided an extra layer of security - after all, what if Han Fei missed something while checking on his own?

With Xu Mo's hacking skills, breaking into a building's surveillance system was quite simple.

He managed it in just a few moves.

Finding the footage from the camera at the rooftop stairway entrance, Xu Mo adjusted the time settings and began watching at increased speed.

Thanks to his enhanced eyesight and mental capabilities, he could review the footage much faster than Han Fei.

It took him only half an hour to go through all forty-eight hours of pre-incident footage.

After watching it, Xu Mo furrowed his brow.

In the forty-eight hours before the incident, there wasn't a single person who had gone up to the roof and not come back down...

To ensure he hadn't missed anything by watching too quickly, Xu Mo reviewed it again.

This time he slowed down the playback speed slightly.

It took him an hour to go through the footage again.

But the result was the same.

In the forty-eight hours before the incident, there was no one who had gone up to the roof and not come back down. Everyone who had accessed the roof had invariably come back down within the time it takes to smoke a cigarette.

Now there were only two possibilities.

Either the killer had incredible endurance, enough to lie prone on the roof for more than forty-eight hours just to commit murder.

Or Xu Mo's guess was wrong, and the killer's method wasn't what he had imagined at all.