The police are confident escaped murderer Phillip Smith will be sent back to New Zealand - but are not sure how long the process will take.
Smith, 40, fled the country a week ago while on a 72-hour release from prison. He used a passport issued under his legal surname of Traynor to fly first to Chile, then on to Brazil.
Smith was jailed in 1996 for stabbing to death the father of a boy he had been convicted of sexually assaulting.
He was detained at a backpackers' hostel in the Rio de Janeiro neighbourhood of Santa Teresa about 2am NZ time today.
Assistant Commissioner Malcolm Burgess said at a press conference today the capture of Smith had an "element of luck" but also displayed good policing.
He said there were three ways of getting Smith back to New Zealand - deportation, extradition or him voluntarily electing to leave Brazil.
Mr Burgess said he could not say what the most likely option was, as it still needed to be worked on with the Brazilian authorities.
"We clearly want to do this legally and make sure we work through the complexities of international law," he said.
"It is a case of doing what's right rather than what's convenient."
Mr Burgess said he believed Smith breached immigration law when he went through the Brazilian border, and there were grounds for deportation.
He did not have the details of how Smith broke immigration law but said it was likely to be a failure to declare any previous criminal convictions.
Mr Burgess could not say how soon Smith could be back in the country.
"It may be quite quickly or it make take a little longer," he said.
"That's something that authorities here, including MFAT and justice and the Brazilian authorities, are working through this at the moment."
He would have a better idea of timeframe once the process of bringing back Smith to New Zealand became clear, he said.
The police in Brazil had a 90-day warrant for Smith's arrest, and he was being held in the notorious Ary Franco prison.
Mr Burgess said Smith's victims would be told what was happening.
"It is very satisfying for us that these victims know Smith is in custody, where he should be, and unable to re-victimise them."
PM welcomes arrest
Prime Minister John Key, who is in Myanmar, welcomed Smith's arrest.
"People will probably be aware there's no extradition treaty between Brazil and New Zealand but there are people that are deported from Brazil to New Zealand," he said.
"We'll just work our way through that legal process now and see what happens next but it's very early days."