God, for His reasons allows evil to exist and allows people to commit terrible crimes in His name.
How can we know that people did not falsely re-write the bible in His name. The bible claims to be the word of god, but how can we know that it isn't a lie created by the same sort of evil men who ran the crusades and the inquisition?
When Jesus Christ cast out a devil from a man that was also deaf and blind. This is what the Pharisees said:
24] But when the Pharisees heard it, they said, This fellow doth not cast out devils, but by Beelzebub the prince of the devils.
 And Jesus knew their thoughts, and said unto them, Every kingdom divided against itself is brought to desolation; and every city or house divided against itself shall not stand:
 And if Satan cast out Satan, he is divided against himself; how shall then his kingdom stand?
The Bible is not divided against itself. It's purpose is singular, to bring Glory to God. Ultimately, you must decide yourself.
Regarding evil. If evil did not ever exist, how could God defeat what has never existed?
Adam and Eve ate of the TREE OF THE KNOWLEDGE OF GOOD AND EVIL. We wanted to know good AND evil. (while knowing the penalty ahead of time) With knowledge comes responsibility and accountability. Therefore, if we sin, the penalty is death. We all die because we have all sinned.