how accurate is it

Read the book written off of his interviews and watche the hbo docs with him, from what I remember I do not recall him killing a high level mob boss out of anger, I could be wrong.

I thought the movie did a poor job of showing how ruthless he really was tho. He was a serial killer long before he was found by the mob, murdering countless men over squabbles far less serious than the one shown at the beginning of the movie. I understand there's only so much time in a movie but I thought it was an important fact about him, that he was a serial killer hired by the mob, not a bad ass who was hired by the mob.

The movie also, surprisingly, left out his most infamous kill, it involves a cave, google it. I thought that would have made the film but I suppose it didn't fit into the narrative.

Overall the movie did his ruthlessness justice for the most part, they touched on his brother and his horrible childhood.