Unless Hart is actually extremely powerful and capable of defending himself from dark magic, there was no reason for him to "investigate" any suspicious people. If anything, due to the current circumstances, he was better off reporting first to his colleagues, then they could decide on an appropriate plan (report back to their higher ups, create a magic tracker, seal the cave, etc.). All in all, Hart's actions just scream suspicious to me. If it weren't for the fact that Maria doesn't sense any dark magic from him, I'd say he was the evil one. Well looking forward to the next chapter.