Greater Manchester Police are questioning a man and a woman about the death in January of 52-day-old Christopher Chapman from Manchester .
The child was declared dead on arrival at Manchester Royal Infirmary after being taken there by ambulance and, when no signs of a suspicious death were found, the body was released to his parents.
A post mortem examination failed to find injuries - thought to include broken bones and head trauma - which were only spotted when X-rays were examined weeks later.
A hospital spokesman said that when the baby arrived there were no external signs of injury and no doctors or officials were told of any reasons for suspicion.
"An X-ray was done at the time of the post mortem examination which was not checked in the normal fashion," he said.
"It was rechecked four weeks later and injuries were found on it and the police were informed.
"We have conducted a full review of what happened and are introducing new procedures to ensure it does not happen again."
A spokesman for Greater Manchester Police said: "Following the death of a 52-day-old Christopher Chapman in January detectives are questioning two people."Reuse content