The doctor who saw him shortly before his death didn't notice his broken back, IIRC. The police didn't act. Social services didn't act. His rotten mother, her rotten boyfriend and their rotten lodger - one or all of them beat and abused and killed him.
There are a LOT of people who are culpable in this case. But Shoesmith is one of them - not only for failing to stop his death but for attempting to cover up her responsibility. As are some of the staff at Great Ormond Street. The doctor who missed his injuries was working for a GOSH clinic where the senior consultant had protested repeatedly that it was understaffed and unsafe. She was bullied and suspended. GOSH management also tried to cover up their role in his death. The then chief executive was a doctor herself, who clung onto her job for ages.
One of the very few people who emerges with any credit is that consultant, http://www.telegraph.co.uk/news/uknews/baby-p/7280085/Baby-P-whistleblower-being-hounded-out-of-Great-Ormond-Street-Hospital.html Kim Holt. Who hounded out of her job.
The lesson of the story seems to be that incompetence and negligence are rewarded - see the then chief exec of Great Ormond Street and Shoesmith - while doing the right thing is punished - see Kim Holt.