I’m not really concerned with the details of this particular story, but just as a general matter, anger is not opposed to love (nor is it identical with hatred). Indeed, sometimes one ought to be angry on account of evil done, and to desire earthly punishment to be visited upon the evildoer.
Anger should of course be moderated by reason, and only directed at the evildoer, not to people who are not responsible for it. However, there’s nothing virtuous about actively spreading nonsense (e.g. “religion is irrelevant” regarding a religiously motivated murder).
Also, forgiveness is not contrary to righteous anger. One can desire the eternal salvation of an evildoer while still wishing a just punishment, even of death, upon him.