The police had identified my patient,Mark,as the serial killer.
However,he vanished from the building where I lived.
The police retrieved the surveillance footage,but they found no video or trace of him leaving the building.He just seemed to evaporate.

His name is Mark.He was my patient.
He remained as calm and composed as usual.
The first time I met him,he didn't resemble my previous patients who exhibited significant emotional ups and downs.Instead,he articulated his thoughts in a highly logical manner.
Through the course of psychological treatment,I uncovered some fascinating insights into his past.
At the age of 12, he witnessed his father's abusive behavior. During a violent confrontation, his mother, in a desperate act of self-defense, severed his father's head in his presence.
Then the police took his mother away.After an investigation,she was charged with intentional homicide.

Consequently, his mother was convicted and sentenced to death.
After losing both parents,he was sent to an orphanage and didn't leave until he graduated from high school.
However, this traumatic incident cast a long-lasting psychological shadow over him.
Moreover, he was not only my patient but also my accomplice in our collaborative endeavors.

Upon entering the house, I glanced around and my gaze settled on a spot in the cloakroom.
“Mark must have left by now,” I mused to myself.
The reason why the police couldn't find the surveillance footage of Mark leaving the building was that he really hadn't left.
When the police were searching my house,he was in the house across the door.
When they searched the house across the door,he came to my house through the connected part in the cloakroom.
And since my house wasn't really the crime scene,the police just checked the surface traces.
How could those fools ever think that the two houses were connected?
"What's wrong,Amanda?"
Alex approached me,"What are you looking at so intently?"
I looked at him wearily,"I'm just a bit tired."
"Then got some rest.I still need to head back to the police station.Remember, don't open the door to anyone, not even the courier.' He fixed me with a steady gaze, and I could sense his lingering concern for me."
He looked at me firmly,and I could tell that he still cared about me.
"Okay, got it,"I replied coquettishly.
Alex left soon.
Just as I was about to fall asleep,a deep male voice came from not far away.
"I never expected him to love you this much."
I didn't need to look.I knew from the voice that it was Mark.
I opened my eyes slightly.He was leaning against the door frame.
I smiled faintly,"You can stay in the guest room.It's very safe."
"When do you plan to reveal the truth?"
"Hmm..."
I sat up,put on a thoughtful look,furrowed my brows slightly,and there was a hint of coldness in my eyes.
"Don't worry. He’s the next."
Mark narrowed his eyes slightly and asked disappointedly,"So we have to wait for another two months?"
"It will be very soon."
Over the next two months,Mark lived right under Alex's nose, occasionally moving between my house and the one across the door.
But Alex didn't notice anything at all.
One day,I joked with Mark,"Does he really deserve the title of 'prodigy in the police force'?"
However,Mark's answer was something I had never expected.
"Because he loves you so much,he trusts you implicitly and would never suspect you."
I paused briefly before bursting into laughter.
"Unfortunately,he loved the wrong person."
"Tomorrow is the 25th,"Mark reminded me.
"I remember,"I replied coldly.
At this moment,the sound of the key unlocking the door rang again.
Mark and I looked at each other,and then I calmly walked out of the room,"You're home early tonight."
"I brought you a cheesecake,"Alex said cheerfully,holding it up for me to see.
I replied happily,"I knew you loved me best."
I accepted the cake joyfully and turned towards the kitchen.My expression instantly turned cold.
I gracefully took out that sharp long knife and stared at the blade,wiping it repeatedly.
"In a few hours,you'll be embedded in his body,"I mused to myself.
"Are you using a meat knife to cut the cake?"He suddenly entered the kitchen,looking bewildered.
"It's been cleaned,"I replied nonchalantly,slicing into the cake with force.
"You're putting so much effort into cutting the cake.Let me do it,"he snatched the knife from my hand.
I smiled at him.
"What are you smiling about?"
I was smiling because in a few hours,he would die by this knife.
"Because you're so considerate,"I said.