At the end of Scream 2 did Sidney break the law?

One of the killers (Mrs. Loomis) is lying dead on the floor after trying to murder Sydney and the others. It's quite likely Mrs Loomis was already dead anyhow but would putting that extra bullet in her head to make sure be a crime? Even if she's still alive (unlikely) at that point she's no longer a threat or would extenuating circumstances come into play here?