Why did heck tate decide not to tell anyone about who killed bob Ewell?

He knew it would be boo radley that would be convicted and he didnt want that. This is because Boo is so shy and by everybody knowing that he defended Sccout and Jem from Bob Ewell, everybody would start giving him attention. THey would give him food and stuff like when Atticus defended Tom and he got food from the colored people. Nobody wanted this for Boo Radley.