The City Of Bones By Michael Connelly

This is the eighth book in the murder mystery series written by Michael Connelly.

Hieronymous "Harry" Bosch is the main character in this book. He is a homicide detective who smokes a lot in Los Angeles. One day, he gets a phone call saying that an old doctor's dog found a bone in the woods. Normally, this wouldn't be a problem. However, this particular bone is the bone of a young boy, 12 years of age, who was physically abused in his early years, Arthur Delacroix, that has been buried 20 years beforehand.
This whole story revolves around finding the identity of this young boy and fining out what happened to him exactly.
After a long period of investigation, they find out that his sister, who claimed to know nothing, was sexually abused when she was younger by her father who had recently gotten divorced . She then took out all of her anger on her younger brother, Arthur.
The father knew all of this and so, when the police came knocking at his door, he confessed to everything, hoping he could protect his daughter. However, his lie was caught and the whole investigation had to start over to find out who perpetrated this crime.

Who could it have been and why did they do it?