Why does Graham plead guilty to a murder he did not commit in the novel, They Wish They Were Us?

When Graham is arrested for the murder of Shaila, he confesses to the crime under pressure from the police, who interrogate him without an adult present and without giving him a break. His parents do not want to fight the charges because they do not want to prolong their embarrassment in the spotlight, so they leave him to be carted off to the Danbury Juvenile Center.