In To Kill a Mockingbird why was Boo Radley locked in the courthouse basement?

Boo was locked in the courthouse basement because he had stabbed Mr Radley, his dad. We are not told why he did this, as it claims "Boo wasn't crazy" (pg 11). "the sheriff hadnt the heart to put him in jail alongside Negroes, so Boo was locked in the courthouse basement" (pg 11)