Investigators examining the shooting of Brazilian Jean Charles de Menezes are "confident" they have all CCTV footage available on the London Tube shooting.
The Brazilian team were briefed by the IPCC for two hours
Independent Police Complaints Commission head Nick Hardwick said some of it would prove crucial to the probe.
But he condemned information leaks on the July 22 shooting at Stockwell, appealing for everyone to maintain a "dignified silence" during the inquiry.
Brazilian officials said they were told some of the CCTV footage did not exist.
"I am the commissioner responsible for this investigation, I still have lots of unanswered questions, I still don't know the truth of what happened.
Jean Charles de Menezes was shot a day after the failed bombs
"I am surprised at the number of people who speak with certainty that (they) do know," he said.
The family should be told any conclusions first, he added.
Brazilians Wagner Gonçalves, Manoel Gomes Pereira and Márcio Garcia were at the briefing in London for an update on the IPCC's progress.
Mr Menezes, 27, died when he was mistaken for a suicide bomber and shot by police at Stockwell Tube station.
'Very poor family'
After the meeting, Mr Pereira, of Brazil's foreign ministry, said the IPCC had mentioned that some of the CCTV cameras on the tube at the time "could be out of order".
"Apparently there are parts of the film which do not exist," he said.
The team will take information from the briefing - about the next steps when the inquiry leaves the IPCC and goes to court, and on the workings of the IPCC - back to Brazil for consideration.
They had discussed the ex-gratia £15,000 payment offered to the family.
Mr Pereira said that did not prevent them suing for compensation over the death, as Mr Menezes sustained his "very poor" family back in Brazil.
Leaked documents contradicted eyewitness reports and initial police quotes suggesting that Mr Menezes' "clothing and demeanour" added to suspicions he was a bomber.
On Wednesday, London Mayor Ken Livingstone suggested disgruntled police officers had sought to undermine Metropolitan Police chief Sir Ian Blair.
He said those passed over for promotion had done "their bit to stab Sir Ian in the back" following the shooting of Mr Menezes.
Mr Livingstone said that if Sir Ian decided to quit over the mistaken shooting of the Brazilian, he would "lock him in the room" until he dissuaded him.
Mr Menezes' family have called for the Met chief to stand down.