The cases under investigation involve 59 victims, some of whom were very young children
A police force has apologised to alleged child abuse victims after it found problems with 30 investigations involving 59 children.
One police officer has been suspended and 11 others have been put on restrictive duties by Essex Police.
Some cases are said to involve a "lack of honesty or integrity" by officers.
Deputy Chief Constable Derek Benson said: "If individuals have failed in their duties then they will be held to account."
The force said 28 cases had been referred to the Independent Police Complaints Commission (IPCC), which was already reviewing two other investigations.
PCC Nick Alston said officers had been accused of "a lack of honesty or integrity"
Most of the cases relate to the work of the child abuse investigation team covering the north of Essex.
Mr Benson said: "We have contacted the families of those involved in these investigations to let them know what is happening and apologise for the undoubted distress.
"We will also look at the possible aspects of why this has happened."
Mr Benson said an experienced retired detective had been brought in to review the "live" investigations being conducted in the north of the force area.
He said the alleged victims included some very young children.
The force apologised last year over its handling of a case involving a five-year-old girl who was raped by a boy, aged 12. The juvenile was given the equivalent of a caution.
Nick Alston, Police and Crime Commissioner for Essex, said Chief Constable Stephen Kavanagh had ordered an "urgent review" late last year after concerns were raised about the quality of investigations.
'Lack of integrity'
"This work led Essex Police to refer a number of cases to the IPCC, to suspend one officer and place another 11 officers on restricted duties," he said.
"The IPCC has announced that it is conducting two independent investigations and a managed investigation of referrals relating to the handling of 28 child abuse investigations which were reported to Essex Police between April 2011 and November 2014.
"These cases involve 59 victims. Some of those investigations involve allegations of a lack of honesty or integrity by officers."
