Death Penalty Research

by Emma
(Massachusetts)

I'm writing a paper on the Death Penalty for my American History class. One of my research questions is, "Why kill a criminal?". I thought of forensic psychology, and how a psychologist can examine a criminal through testing and deem them truely dangerous or possibly insane.

If that doctor was then interviewed on the trial of the murderer they interviewed and confirmed them as such, the criminal would be justified as a death penalty candidate.

But how do psychologists deem killers as psychopaths? what tests do they use? is there a clear, written spectrum defining where a human being crosses the line from normal criminal into dangerous to be living?