If an alien had the power to jump into a human's mind and control the human: how would it be possible to capture that kind of alien?
The alien is in the form a gaseous chemical life form. When inhaled by a human it can take control of the human's life after it reaches the human brain. It has the ability to come out of the human body at will by means of diffusing out of the human body at it wishes.
This alien is basically in gaseous form. So how to kill a alien which is just a gas compound?