A convicted criminal given work at a primary school as part of a court community service punishment went on to sexually abuse a child, police say.
Ian Missing worked as an odd-job man at the un-named school after being convicted of common assault.
The 23-year-old, of Chelmsford, Essex, had previously been accused of sexually abusing a child but not prosecuted.
He indecently assaulted a child during his time at the school, although the attack did not happen there.
Police said in a statement: "Essex Police and the Essex Probation Service share the concerns of the young girl's family as the safety of our community, particularly children is paramount.
"Essex Police and Essex Probation are determined to find out how this situation occurred and will be looking to establish if there are any loopholes in our current processes.
"If these are found then immediate steps will be taken to address them."
The police and probation service have launched a review to determine exactly what happened.
The spokeswoman said Missing had admitted indecently assaulting a child while carrying out the punishment order.
He was due to be sentenced at Chelmsford Crown Court next year.