I don't know who can or can't be "called" and Evangelical Christian as I am in no position to judge a person heart, but mass/serial murder is such an egregious violation of Gods commands (in many ways), I don't care what he did, he can be safely and should be considered an apostate (false convert), Jesus himself said, Matthew 7: 21“Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but the one who does the will of my Father who is in heaven. 22 On that day many will say to me, ‘Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many mighty works in your name?’ 23 And then will I declare to them, ‘I never knew you; depart from me, you workers of lawlessness.

And these are those who appear to be Righteous and not serial killers.