Alex looked around, every piece in the room coming together to form a whole picture.
The murder happened at exactly 6:45pm, there was no break in. Every act had been carried out swiftly and with precision, everything made sense except a single minor detail, a half drank cup of coffee.

That particular item that the murder always left behind always left Alex wondering why?
Over the last months, three murder cases with that half drunk cup of coffee left.
Alex had tried to find the killer but whatever he did, it seemed like the person was always one step ahead of him.
He was in a race against time because the longer the case was left unsolved, the more murders would occur.

Source
As he sat in the café, sipping his own cup of steaming coffee, he mulled over the details.
All the cup of coffee were bought from that very café. Unfortunately the barista just like the other time said the same thing, no one suspicious had made an order.
He looked around the crowded shop. He was in a race with the murder to solve the case before he stroke again.

He couldn't shake off the feeling that the killer was watching him with every sip he took.
Alex's train of thought was interrupted by a loud crash on the other side of the café. He spun around in his seat, gun ready at hand, only to see the barista picking up a tray of dropped cups.
"I'm really sorry. I don't know how I've stayed so long in this job with how clumsy I am." She laughed nervously.

Alex nodded his head, "It's fine."
She stood for a minute, "I'm really sorry I couldn't be of more help to you. I know everyone that comes in here. No one out of the ordinary."
"I understand. I will find him eventually, they always slip up."
"How do you know it's a guy?"
"The last three victims have all been women. What motive would another woman have?"
The Barista's hand went to her locket and Alex's eyes followed.
"That is a beautiful locket."
She smiled, "Thanks. My friends gave it to me."

One day later, Alex stood, staring down at the now lifeless body of the Barista. The killer had struck again, and he had lost the race yet again.
"Sir, did you hear what I said?"
"What?"
"I said the killer left the cup of coffee again but it was untouched this time."

Alex's mind raced as he absorbed the detective's words. Then something clicked, it wasn't the killer leaving the coffee behind, it was the victims.
Why hadn't he ran fingerprints tests on the cups earlier?
He had been so focused on trying to decipher the clues that was left by the killer that he didn't think to interlink it.
All the victims shared something in common, their love for coffee. His eyes caught the locket again and he knelt down. A note was inside with a single sentence, Catch me if you can. I'm right in front of you.

Weeks went back and one more murder happened. Alex sent the cup this time to the forensic team. The forensic team discovered a microscopic substance on the rim of the coffee cup. It turned out to be a rare, tasteless poison. That was why there was never a struggle, the killer had been poisoning them unknowningly.
But then the question came why?

Alex sat in his office, all the now empty coffee cups in front of him. Why was this the one case he couldn't crack?
In a moment of frustration, he angrily tossed the entire evidence to the floor and everything went crashing to the ground.

One particular item fell and Alex's eyes went to it.
He picked it up staring at the picture in the locket. Six girls, four of victims stared back and suddenly everything came into play, all the pieces finally came together.
He picked up his jacket, making a phone call to ask them to find the next victim. While he was in his car, he got the address. He increased his speed in a race to save her.

Alex stood for a minute before he finally spoke.
"Seems like you didn't catch her at home."
The killer froze, the cup of coffee in her hand.
"I was getting it all wrong, they didn't love coffee, you are the one with an obsession."
"Everything fell into place but I still have a question why?"

"Twenty years ago, they thought it would be funny to lock me in a room for hours. I can still hear the laugher echoing in my head. Eventually they let me out and in a moment of confrontation, I fell into a pool. I was dying and the five of them stood above me still laughing."

Then after the incident, after they watched me die, they moved to different cities and changed their names so no one would link them to what happened. But I did and I watched with pleasure and laughed as they all struggled before dying."

"So why did you fake your own death?"
The barista smiled, "I thought it would be funny. How stupid do you feel knowing I was right in front of you the whole time/?"
"It's over, you are under arrest."
"I'm not going anywhere until Clara is dead."
It happened in a spun of seconds, the shot sounded and the barista dropped to the ground.

Alex stood by her graveside. The Barista had played a game of cat and mouse well but she had gotten to cocky.
Clara walked up beside him, She sucked in a breath, "We didn't mean for it to happen. It was supposed to be a prank, then things took a turn. Now the four of them are gone. And I could have—"
"But you are not."
She sighed, "Thank you detective."
Alex tipped his hat and walked away, onto the next case.