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Karel Sroubek returned to Czech Republic in 2009 for one night, his mother Mila has confirmed to Checkpoint.
Questions were raised about whether the convicted drug smuggler returned to his homeland, after court documents revealed he travelled to Europe in 2009.
Sroubek, who is in prison, was liable for deportation but Immigration Minister Iain Lees-Galloway gave him a reprieve when he granted him residency under his real name in September. He later confirmed he spent one hour reading the case notes before making his decision.
The Minister has previously refused to discuss the reasoning behind his decision, but his mother Mila said her son's life would be in danger if he returned home using his real name.
"Because he acted as a witness against a person who murdered, minutes after it happened he gave testimony about it to police… he was immediately threatened to change his testimony so that the person who committed it, that his sentence would be lowered."
In an exclusive interview with Lisa Owen, carried out with an interpreter, Mila confirmed he had returned home in 2009 under the name of Jan Antolik, the false identity he used to first enter New Zealand in 2003 and gain residency in 2008.
Mila said her son returned home for one night, via Germany in 2009, without her consent.
"It was his impulsive decision at that moment because he was very home sick, but we insisted that he immediately return to Germany.
"He travelled under someone else's identity, Jan Antolik. And that was the main reason why. It also offered him a little bit of cover."
When asked if she believed he could be killed if he returned using his real name, she replied: "That could happen. Yes. I really believe that. There are many cases like that in the Czech Republic."
She accepted the situation looked bad, but said he was young at the time and wasn't thinking "straight".
"I can understand his feelings, that he was homesick, and wanted to visit his own home even for a very short time."
But she said it would be different if he travelled home using his real name, saying they did not trust the justice system or the police to protect him.
'He is not a bad person'
Sroubek has amassed several companies and a house in New Zealand, and is now in prison for importing 4.9kg of MDMA.
When asked if her son was a gangster, Mila said he "absolutely" was not, but media were trying to make out that he was.
"I am convinced about it and they are, there is no proof and gangster is something totally different than my son is… I can't. I don't even want to imagine that. It's terrible. It's terrible."
While she didn't want to believe he was guilty of importing drugs into New Zealand, she said he had been convicted so she had to accept that.
She said his wife has filed for divorce after entering a relationship with Mark Davey, who she said was a member of the National Party.
When asked why she thought her son's case had become political, she answered: "In the beginning it was personal interest of my son's wife and her new partner, but then it became political because the National Party now can use it to increase pressure on the current minister."
The National Party has called for the minister to stand down, saying he should have never made the decision he did.
"I would ask the minister to give him one last chance to prove that he is not a gangster, that he is not a bad person and if he did anything he is now paying the consequences and he is trying to straighten all that up."
Mila came to New Zealand on a visitor visa, which she hoped to extend so she can stay on to support her son.
Speaking in English, she said: "I love my son. As every parent and I wish him a better life in the future. Safe, safe life with a loved partner, change his life forever. Forever. Because he is not a bad person."
Mr Lees-Galloway has demanded his officials review all information provided to him about Sroubek's case, following "new information" which he received.
Checkpoint has made repeated attempts to contact Sroubek's wife and her new partner Mark Davey, but they have not responded to texts, messages or emails
National Party MP's Michael Woodhouse and Mark Mitchell said they did not know Mark Davey.
National party president Peter Goodfellow was also contacted, but he did not respond.
Mr Davey stood in the 2016 Auckland local body elections on the centre right ticket of Auckland Futurem, which is connected with the National Party and at the time was backed by former National Party presidents.
Mr Lees-Galloway also declined to be interviewed.