I am about to leave my agnostic cave and explain to you why what you are saying is contrary to the definition of "evidence".
God is a very bland, and varying term. Your train of though is that God is always good, this massacre is bad, therefore God must not exist. However, God does not necessarily have to be a good-being in our sense. Perhaps it knew something we did not. Maybe it screwed up (Ancient Hebrew, Greek and Norse mythologies had gods fucking up all the time, not to mention gods that could have used a condom or two). Or maybe God is so tremendously complex, that there is no hope of ever understanding it. There is no "evidence" to suggest otherwise, but there is not any to support it either.
I do not currently believe in god, however there is still a possibility it/they exist.