Two senior Brazilian officials have visited Scotland Yard to discuss the investigation into the shooting of Jean Charles de Menezes.
The 27-year-old Brazilian was killed by police at Stockwell Tube station on 22 July after officers wrongly linked him to the attempted bombings a day before.
Leaks from the Independent Police Complaints Commission have cast doubt on claims Mr Menezes resisted arrest.
His mother has said action must be taken against the Metropolitan Police.
"They took my son's life. I am suffering because of that," she told BBC News.
"I want the policeman who did that punished. They ended not only my son's life, but mine as well."
Arriving at Heathrow Airport, Brazilian government official Marcio Pereira Pinto Garcia said he and colleague Wagner Goncalves wanted "to understand a little bit better how the system works, how the IPCC works and what's the legislation that's going to be applied".
At Scotland Yard they met Deputy Assistant Commissioner John Yates, and Commissioner Sir Ian Blair, as well as other senior officers.
The Met said DAC Yates had reiterated the apology he had made on a personal visit to Mr Menezes' family in Brazil.
A spokesman said the meeting had been "positive and constructive", covered the protocols of the investigation, but had not gone into specifics because of the IPCC inquiry.
The Independent Police Complaints Commission (IPCC) said the officials would not meet its representatives until Wednesday.
Up to 200 supporters of Mr Menezes' family attended a protest vigil at Downing Street to mark a month since the electrician was shot.
His cousin handed in a letter to the prime minister calling for a public inquiry.
Emerging from Downing Street Alessandro Pereira was greeted with cries of "no justice, no peace" from the crowd.
Surrounded by a scrum of journalists, he told the crowd: "Every day we discover more and more lies.
"We have heard too many, we simply demand truth and justice."
Mr Menezes' cousin, Alessandro Pereira, gave a letter to Mr Blair
Mr Menezes' family want Sir Ian to resign for incorrectly linking the shooting to the attempted bombings early on.
On the day of Mr Menezes' death, Sir Ian said the shooting was "directly linked to the ongoing and expanding anti-terrorist operation".
Sir Ian has told the News Of The World it was 24 hours before he learned the Brazilian was wrongly shot dead leading the family's lawyer to express "incredulity" that he made statements without knowing facts.
Leaked documents from the police investigation into the death appeared to contradict initial police and witness statements about the incident.
Scotland Yard was quoted as saying that Mr Menezes' "clothing and behaviour" added to suspicions.
Sir Ian has said he will not step down over the Menezes case
But a leaked photograph of the body of Mr Menezes on the Tube shows he was wearing a denim jacket - not a bulky one as previously described by an eyewitness.
Giovanni da Silva, Mr Menezes' brother, called on the Metropolitan Police to "show all the video from the Underground so the world can see what they did to an innocent man".
On Sunday, a spokesman for Tony Blair said he fully backed Metropolitan Police Commissioner Ian Blair over his handling of the case.
Meanwhile, Diana Gorodi, whose sister Michelle Otto died in the Russell Square attack on 7 July, said she would be upset if the police were forced to make changes to their "shoot-to-kill" policy, which she said made people feel safer.
She said she was sorry about Mr Menezes' death, but added that the "hysterical" criticism of the Met had shifted attention away from the deaths of 52 people in the London bombings and "crucifying" Sir Ian would not achieve anything.
Scotland Yard has confirmed that an offer of £15,000 - which it stressed was an "ex gratia" payment which would not affect any further compensation or legal action - had been made to the Menezes family.
The family rejected the offer, which is said to have caused them offence.
Their solicitor Gareth Peirce said the offer may have been a "deliberate attempt to ensnare families into inappropriate agreements or inappropriate decisions".