In November 2013, Essex Police was given information from the Child Exploitation and Online Protection Centre (CEOP) about Martin Goldberg.
The force did not realise he was a teacher until September this year.
Essex's police commissioner said "an ambiguous phrase" was behind the delay - but refused to clarify what it was.
"It is believed that what went wrong was a misinterpretation of an ambiguous phrase used by CEOP... as they passed the material over," Nick Alston said.
"However, that detail is rightly being looked at by the Independent Police Complaints Commission (IPCC).
"It would be wrong of me to pre-empt that investigation," he added, when asked if he could reveal the phrase used.
Goldberg, deputy head of Thorpe Hall School in Southend, was found dead the day after being interviewed by police.
His name was on a list of 35 intelligence "packages" passed to the force by CEOP 10 months before his death.
The centre had received the information from police in Canada in 2012, after a company selling videos of naked children was investigated.
But he was not identified to Essex Police as "high risk", a force spokesman said.
When they discovered his occupation, officers applied for a search warrant - which was declined - and visited Goldberg at his home.
Mr Alston said Essex Police had changed its policy as a result of Goldberg's case.
He said when intelligence was received, occupation checks would be carried out straight away to determine if they worked with children.
"We needed to identify any key issues immediately, and Essex Police needed to act to address those matters and help protect children from harm as soon as possible," Mr Alston said.
A spokesman for CEOP said he could not comment on the case due to the IPCC investigation.
A teacher who took indecent photos of pupils was not investigated immediately because of a "misinterpretation of an ambiguous phrase", it has been claimed.