Nobody is saying that not a single Christian ever murdered someone.Is this where I say "yes they do?"
Here's a random pastor, a Baptist minister apparently, charged with murder:
An Alabama pastor has been charged with the murder of his wife who was found dead in their home in July 2013, according to a breaking story posted on The Alabama Baptist newspaper's website.www.baptistpress.com
Was he a Christian before the murder? How about after the murder?
The point is that it's the extremely rare exception.