Mr Searle said he had been on the phone to Mr Slater’s “devastated” mother Debbie Duncan when the identity of the remains was confirmed.
He said: “Debbie broke down on the phone when she heard that news. When the confirmation came through all hope was gone.
“There’s no looking back now, no ‘Maybe it’s the wrong person’ or ‘Maybe it’s going to change’, it’s there in the cold light of day.”
He said the family was keeping busy, making plans for Mr Slater’s funeral and repatriation, which he said his organisation would be helping with.
“Debbie has told me if she is not doing something she will just fall apart,” he said.
Mr Searle said the family was likely to travel back to the UK on the same plane as Mr Slater’s body.
And he said he would be speaking to the Home Secretary about the harmful nature of much of the online activity around the case.
“I’ve been in this job for over 20 years and I have worked on thousands of cases and I have never seen anything like this level,” he said.
“It seems like it’s ramped up recently and it’s something I feel passionately about, something I am going to be talking to the home secretary about in the coming weeks.”
