Immigration NZ was told in 2012 that Czech drug-smuggler Karel Sroubek had been back to his home country in 2009, but this was not included in the original file to the Immigration Minister because the information was somehow overlooked.
The revelation is among hundreds of pages of documents released under the Official Information Act today - the last Friday before Christmas.
The documents show immigration officials referred to Sroubek having the "luck of the charmed".
Sroubek's return to the Czech Republic was a key part of Immigration Minister Iain Lees-Galloway's decision to review the case because, if true, it undermined Sroubek's claim that his life would be in danger if he were deported.
Lees-Galloway had initially granted Sroubek residency despite Sroubek being in jail for drug-smuggling, but overturned that decision after the review.
Immigration NZ general manager Stephen Dunstan has previously said that Immigration NZ knew Sroubek had been in and out of New Zealand, but was unaware he had returned to the Czech Republic.
But an email from a Customs intelligence analyst, whose name is redacted, to Immigration NZ compliance manager Bernard Maritz in March 2012 said that Sroubek - also known as Jan Antolik - was in the Czech Republic in 2009.
"On 24/09/09, ANTOLIK arrived at Auckland Airport and was subject of a search by NZCS (Customs Service). It was reported that he had travelled Auckland - Bangkok - Frankfurt return," the email said.
"From Frankfurt he had hired a car and driven to the Czech Republic. The purpose of this trip he claimed (redacted)."
The Customs analyst had written to Immigration NZ two weeks earlier after reading about Sroubek's case in the media.
"ANTOLIK is a person of interest to NZ Customs and there are a number of reports that may be of mutual benefit to both departments, particularly with his claim that he would be in danger if he was deported to the Czech Republic."
This information was forwarded on, but seems to have slipped under the radar and was not included in the file that eventually went to Lees-Galloway prior to making his intial decision to grant residency.
Also among the documents is an email from Immigration NZ staff describing Sroubek as having the "luck of the charmed".
Following a report in the Herald in 2017 about Sroubek's failed bid to appeal his conviction for drug-smuggling, Immigration Technical Specialist Janene Smith emailed a colleague about the case.
"We prosecuted him for using a false identity but Mr Antolik seems to have the luck of the charmed - the Judge discharged him without conviction so that he wouldn't be deported," Smith wrote.
The Sroubek case created a political storm over the past two months after it was first revealed that Lees-Galloway had cancelled Sroubek's deportation liability and granted him residency in his real name in September.
This was despite Sroubek having two grounds for deportation: a conviction for smuggling MDMA, and for falsely using a passport to gain a resident visa.
After initially defending his decision, Lees-Galloway ordered Immigration NZ to review the case after being told that Sroubek's estranged wife may have retracted her earlier support for him, and after court documents showed that Sroubek had been back to the Czech Republic.
After the review, Lees-Galloway issued a new deportation notice to Sroubek on the basis that he should never have been granted a visa to be in New Zealand in the first place, given his prior convictions in the Czech Republic.
Sroubek is appealing the decision.
Karel Sroubek flees Czech Republic as witness to a murder. Enters New Zealand with false passport in name of Jan Antolik.
2008: Gains residency under the name Jan Antolik and represents his new country as a kickboxer.
2009: True identity discovered when Czech police contact their counterparts in NZ.
2010: Arrested with two Hells Angels gang members on aggravated robbery and blackmail charges. Acquitted on all charges.
2011: Jury finds him guilty of using false passport and giving false details to Immigration officials. Arrested soon after as part of Operation Ark, a covert investigation into Ecstasy-like pills.
2012: Judge discharges him without conviction on false identity charges so Antolik is not automatically deported.
2014: Convicted of manufacturing Class-C drug from Operation Ark arrest. Conviction overturned but Crown abandons second trial. A few months later, arrested importing 5kg of MDMA, a Class-B controlled drug, used in Ecstasy.
2016: Convicted of importing MDMA and jailed for five years and nine months, but identity kept secret by sentencing judge.
2017: Name suppression lifted.
2018, Sept 17: Parole Board declines early release.
Sept 19: Immigration Minister Iain Lees-Galloway cancels Sroubek's deportation, grants resident visa in his real name with conditions.
Oct 26: Sroubek claims financial interest in $2.3 million Remuera property, which is allegedly burgled a few days later.
Nov 1: Lees-Galloway says he did not know of court documents showing Sroubek had returned to Europe in 2009. Orders Immigration NZ to investigate.
Nov 6: National reveals court documents that show a man and his family were in a witness protection programme because of alleged actions by Sroubek and two other men with connections to the Hells Angels.
Nov 8: National alleges during Question Time that Sroubek made a threatening phone call to his estranged wife on May 3.
Nov 8: Sroubek releases statement saying he had nothing to with the alleged house burglary, and was acquitted in the trial that involved the witness protection programme.
Nov 8: Pressure intensifies on Lees-Galloway after he concedes he didn't read the entire Sroubek case file and made his decision in under an hour. National calls for his resignation.
Nov 9: Jacinda Ardern continues to have confidence in Lees-Galloway, but wants the process around deciding these cases improved.
Nov 13: Sroubek's mother Mila Sroubkova tells Radio NZ's Checkpoint that her son is not a gangster, and fears for his safety if deported are very real.
Nov 28: Lees-Galloway issues a new deportation liability notice to Sroubek, meaning he will be deported after finishing his jail term. Sroubek is appealing the decision.
Dec 12: Jacinda Ardern reveals that Richie Hardcore, a friend of Sroubek's, texted her after news broke about Sroubek being granted residency. She did not reply, and declines to release the text, citing privacy reasons.
Dec 16: Sroubek says he has never threatened his estranged wife and she did not wrote a support letter for him under duress. Refers to the whole matter as a marital dispute turned into a political football.
Dec 18: Sroubek's estranged wife releases a phone call between her and Sroubek in which he appears to become desperate and frustrated, and asks if she wants him to send "somebody to talk" to her.
Dec 20: Sroubek responds saying it was a cry for help, not a threat.
Dec 21: Government releases documents in response to Official Information Act requests.