IT was a question senior police officers refused to answer.

How could a paedophile teacher carry on filming boys undressing in his school’s changing rooms for eight months despite police knowing he had purchased videos of children on the internet?

In the days that followed Martin Goldberg’s suicide in September 2014, officers hid behind the imminent investigation by the Independent Police Complaints Commission.

Now, the Echo can reveal the full extent of the catalogue of errors, as well as the uncertainty and stress endured by investigating officers as they struggled to cope with staffing shortages and increased workloads.

The 46-year-old deputy head of Thorpe Hall School, in Wakering Road, Southend, could have been unmasked as a pervert by a simple Google search in July 2012.

Police in Toronto, Canada, had passed 35 names onto the UK’s Child Exploitation Online Protection (CEOP) centre after an investigation into a website selling naturist videos.

The PCC report does not say why it took the National Crime Agency department until November 25 to forward the 35 names onto Essex Police, which then opened Operation Spade.

But what is clear, is that when the Essex Police Online Investigation Team received the names they did not know what to do.

The intelligence arrived with a briefing that said checks on some individuals had been carried out.

But the it ended by saying: “We would urge forces to undertake their own risk assessment jointly with Children’s Services, especially, if initial system checks identify that the purchaser of these images has direct contact with children or holds a position of trust which would allow access to children.”

Disastrously, the unit’s Detective Inspector emailed his Detective Superintendent to say CEOP had definitely already carried out a risk assessment.

It was not until December 11, when CEOP clarified once again that it had not checked every name on the list that Essex Police's online team created 35 investigation records, including one for Martin Goldberg.

The Detective Superintendent then cross-checked the invoices for each suspect against the incomplete list of titles provided by Toronto Police.

He was able to eliminate 13 men whose purchases were not of illegal material and one suspect who was already under investigation by the online team, leaving 21 suspects.

Goldberg was one of them.

But just as the net appeared to be closing on the paedophile officers made another blunder.

Contrary to national police guidance, the Detectivc Superintendent failed to consult several databases, including the Disclosure and Barring Service (DBS), which carries employment information.

Instead, he answered an eight question form which included a question about whether Goldberg had access to children at home or at work.

It was not until September 4 that an under-pressure civilian Investigations Officer contacted the DBS.

Six days later the service got back to her- Goldberg had made an application in 2005 over his ongoing employment as a teacher in Southend.

She asked a Detective Constable to check the school’s website to see if the paedophile still worked there.

He did, and Goldberg was immediately elevated to a high risk.