I still think personally that accardo was an informant.in the book family affair they talk about how a guy that had built accardos house had secretly given the blueprints to the fbi 2years later and somehow accardo found out about it and had him killed.how did he find out? I doubt the fbi went and told him look what ur builder just gave is.unless he had a relationship like flemmi n bulger or scarpa sr had with the fbi