Immigration Minister Iain Lees-Galloway has admitted he took only an hour to decide to let Karel Sroubek stay in New Zealand and did not read the entire case file.
Sroubek is at the centre of a controversy after Immigration Minister Iain Lees-Galloway confirmed his residency and stopped him from being deported.
Sroubek was jailed in New Zealand in 2016 for five years and nine months for importing the drug MDMA and entering the country under a false passport.
In response to questions in Parliament, Mr Lees-Galloway confirmed he made his decision on the same day he received the file.
He later told reporters he took "an hour or so" to make up his mind and said that was "much, much longer" than he'd taken on other cases.
"I took the time that I felt was necessary. I certainly asked questions. I certainly looked closely at different aspects of the file," he said.
Mr Lees-Galloway said he went through the summary with his officials, but admitted he did not read the file in its entirety before making his decision.
"I read the aspects of the file that I felt were necessary to make the decision that I made."
The minister defended his decision-making, saying he followed the exact same process as the previous government.
"This is the usual process for these decisions."
Mr Lees-Galloway said he'd since read the full file "several times" and stood by the decision he made on the basis of the information provided.
Asked whether in hindsight he would have taken more care and time, he insisted he was "thorough" and had given the case "due consideration".
"That's the job."
National has been demanding the minister stand down, saying it's now obvious he didn't do his job.
National MP Michael Woodhouse said the "extraordinary development" proved the minister had been reckless.
"This was a terrible decision made by an arrogant minister who didn't look at his papers properly.
"Certainly a decision to overturn a deportation like this should have been much more carefully considered."
Speaking on behalf of Prime Minister Jacinda Ardern, Winston Peters, replied that all the information available at the time would be looked at and that he should have been deported from the country, according to the evidence starting to emerge now.
The Czech Republic's Ministry of Justice is now preparing an extradition request.
In a statement it said as well as seeking prosecution for attempted bodily harm and disorderly conduct, Sroubek had a conviction for disorderly conduct, damaging another's property, and attacking a law enforcement officer.
"He is required to serve a sentence of imprisonment of four years and six months in relation to those convictions," a spokesperson said.
Mr Lees-Galloway has ordered an investigation into the information he received from officials, which led to his decision to let Sroubek stay in New Zealand once he is released from jail.
The investigation has been given a three-week deadline, but both the prime minister and Mr Lees-Galloway want it done a lot more quickly than that.
Sroubek first public comments since controversy
In a statement earlier today, Sroubek says much of what has been said about him and his circumstances does not present the true picture.
"In 2010 I faced charges. I was properly acquitted at trial, as were all of the other people charged," he said.
A witness in the case made an appeal to the court in 2010 to give evidence remotely, because of fears for his safety.
The judge rejected the appeal but in his decision detailed two assaults against the witness - one involving Sroubek, and a second with Sroubek and three co-accused, who had links to Hells Angels.
The witness, his wife and child ended up in police protection.
"Comments made about that case in the media are not balanced, and in particular do not reflect that the key prosecution witness' evidence was discredited," Sroubek said.
By Craig McCulloch