|Essex Police Headquarters|
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.
|Essex County, England|
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.
The girl, who is now eight, wrote to the police: "When I was five something very bad happened and it was your job to make sure he was properly dealt with and punished."
"But you didn't do your job and you let me down."
Mr Alston said: "It has left a victim and her family utterly bereft of justice. Leads to other potential offences were not properly investigated at the time.
"Furthermore, it may have caused people in our county who need the help of Essex Police wondering if they can trust them."
Essex Police said the rape was reported in August 2011. Details of the letter written by the victim emerged in a story in the Mail on Sunday newspaper.
Officers wrongly claimed that they had reported the case to the Crown Prosecution Service, failed to have the rapist's name added to the Sex Offenders Register and neglected to take fingerprints, DNA samples or photographs, the newspaper said.
In a statement, the force said: "The offender, also a child, was interviewed the same day and in November 2011 was given a final warning, the juvenile equivalent of a caution.
|Police and Crime Commissioner Nick Alston|
'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."
Deputy Chief Constable Derek Benson: "There were issues around supervision and quality of the investigations"
Some of the investigations which have been referred to the IPCC are based on allegations of historical abuse, dating to the 1960s and 1970s.
The IPCC says its investigation will look into whether officers failed to:
consider the safeguarding of children
progress investigations properly, including not arresting suspects and delays
refer cases to the Crown Prosecution Service
Mary Cunneen, IPCC Commissioner for Essex, said: "Child abuse ruins people's lives, so it is important police get these investigations right and victims feel confident their cases will be properly handled.
"It is vital our investigations are able to establish what happened in the north child abuse investigations team investigations, and why."
The IPCC said it was already investigating the conduct of five officers from the north child abuse investigations team following referrals from Essex police last August and October.
These concern an allegation that a police officer fraudulently signed a complainant's signature, and how officers responded to reports a girl was allegedly the victim of child sexual exploitation.
A helpline has been set up for anyone who feels concerned about child abuse investigations carried out by Essex Police. The number is 01245 282103.
From Feb 23, 2015
Eight extra cases have been referred to the Independent Police Complaints Commission (IPCC) on top of 30 already being looked into.
The investigations relate to a team covering north Essex.
Essex PCC Nick Alston said the increase was "distressing". The force has been asked to comment but has yet to do so.
"As the review into the quality of child abuse investigations instigated by Essex Police progresses, regrettably I do not find it surprising that it has identified further cases of concern and fresh referrals to the IPCC," he said.
But he stressed the number of cases being dealt with by the IPCC remained "a small proportion" of the total number of such cases investigated by the force each year.
"I am convinced the force is making real efforts to identify and resolve problems with the quality of child abuse investigations," Mr Alston added.
One of the force's officers was suspended and 11 others put on restricted duties following the force's referral of 28 cases to the IPCC.
|Essex Police chief constable Stephen Kavanagh|