A toddler's death "probably would have been avoided" if police, social services and health chiefs had not returned him into an "unsafe environment", a coroner said.
Two-year-old Joshua Jones, from Runcorn, Cheshire, died on November 6 2007.
His mother's boyfriend, Wayne Davenport, was jailed for six years in 2009 after he was convicted of manslaughter.
Davenport's trial heard that he spent months punishing the toddler and unleashing a horrific catalogue of abuse on the boy. Joshua's mother, Nichola Bowman, was convicted of causing or allowing her son's death and was given a suspended sentence.
Following a five-day inquest at Warrington Town Hall, the coroner for Cheshire, Nicholas Rheinberg, recorded a verdict of unlawful killing.
He said: "Joshua's death on November 6 2007 probably would have been avoided if the three agencies concerned with his safety (Warrington and District General Hospital, Cheshire Police and Halton Borough Council) had taken steps which did not involve returning him to an unsafe environment."
The inquest heard that Joshua was taken to Warrington General Hospital on October 26 2007 by his mother and grandmother, Michelle Littlemore, with a broken arm and a "constellation of other injuries", including bruises to his back and penis. But, despite the injuries "ringing alarm bells" with numerous doctors, social workers and police officers, after six nights in hospital Joshua was allowed back into his mother's care.
After the inquest, Audrey Williamson, independent chairwoman of Halton Safeguarding Children Board, said: "We are going to study very carefully what the coroner has said. At the time we did an in-depth review and looked in detail at the individual agencies and what agencies did collectively in their work with Joshua. We learned some lessons and the coroner has heard that.
"If there is more to learn I would like to assure you that we will take those lessons on board, we will implement them and make sure they will continue to be implemented."
Bowman did not attend the hearing but her mother, Ms Littlemore, said after the inquest that her daughter had "taken responsibility" for what happened "on her own shoulders" and said she hoped the agencies involved would do the same. She said it was "good" that the "errors" that were made in relation to Joshua's care were uncovered but said "they shouldn't have happened at all".