What are the symptoms of psychopath?
How can we know that someone is a psychopath patient?
I'm sure you mean "the early signs of psychopathic behavior". If that's the case then use http://www.bostonmagazine.com/2012/06/ten-signs-dealing-psychopath/ for simple answers. Research it further if you want a more in-depth answer.
You can't know for sure.
Self centeredness... Conduct disorder... Lack of empathy for others... Narcissism... Selfishness... Although you can confuse being a psychopath with being a sociopath or just plain narcissistic...
I do not know the exact details but make sure you do not confuse psychopath with sociopath.