Well he wouldn't need to be particularly heartless to do it if the animatronic was close enough behind Connie. Rather than let Connie in and risk Bonnie/Freddy getting in as well, therefore condemning everyone in the room to death, just lock them both out and let Connie (supposedly) be sacrificed to save the others. Yeah, that'd be a great scene, heart-wrenching and emotional for those inside the room and particularly for the one left outside. Ahh, I'm so evil; never let me play God if you know what's good for... well, anything and everything.