SCP-JJT-999 The Unknown Killer

Introduction
SCP-JJT-999, also known as The Unknown Killer, kills people, but the scary thing is that no one knows how. Every day one person in the word drops dead on the ground, without any sign of what could have killed them. No outside or inside wounds are on their body, their organs are in perfect condition, they don't have any kind of poison in them, or any kind of germs, or anything else.

Exactly 1 hour 36 minutes and 7 seconds after the target is killed, a sign comes out of their body, reading "Their soul is mine." Then, inside of the body of the victim, their heart is gone, and the sign works like a fully functioning heart.

How to Keep Contained
It is not known if SCP-JJT-999 has a physical form or not, making it impossible to keep them contained. But they have a chamber for them in case they can be contained.

Extra Information
Nothing else is known about SCP-JJT-999