Middleton says his 16-year-old son had penned a letter to Faafoi and demanded he deliver it.
"I didn't ask him to do that, he just did it of his own volition really. He wasn't having it, he just said 'I'm going to write this' and you'd better hand it over to him."
His son was upset at the thought his father might have to leave the country.
"We're pretty close," Middleton said.
In his letter, Middleton's son said his dad was "a really good bloke who has helped me through the toughest times in my life".
His father was the main breadwinner in the family and without him "we will be left with nothing. It will cause the ultimate downfall of our family as we know it".
He urged Faafoi to take his letter to heart.
Middleton, who lives in the Hutt Valley with Karla's mother Veronica, said he still had no real idea why he was being threatened with deportation. He moved to New Zealand with his family in 1962 as a four-year-old .
"They say they don't have any documentation on me before 1986 so I'm here to give them that.
"It lays out the time when I came here from 1962 with my parents right through to the present day.
Immigrants from the United Kingdom were granted permanent residency if they arrived before April 4, 1974.
Faafoi's office said today the Minister was still considering the application.
Middleton said he was hopeful of a positive outcome, "sooner rather than later".
He declined to talk about whether he would seek redress over the time he spent in custody if the Minister found in his favour.
"To be taken out of my place of work and put down the hole at Wellington Central (police station) is a bit heavy-handed. I think it could have been handled differently. I'd already agreed to come in. I'm not running anywhere and I'm certainly not hiding."
Middleton said he has been overwhelmed by the support he has received since his story appeared in the media.
"I've received amazing support from all over the world. It keeps me buoyant and it's nice to know it's not just my New Zealand community who supports me but there's a wider community out there in the world."
Middleton was confronted by immigration officers at his workplace last week and told he was an overstayer. They put him into a police cell for 36 hours.
An Immigration New Zealand spokesman told the Herald on Sunday Middleton came to its attention last year and the department prioritised cases for deportation for those engaged in criminality or who posed a risk to the immigration system.
Middleton was sentenced to nine months in prison in 2001 for threatening to kill Karla's killer, Paul Joseph Dally, but the sentence was suspended and he did not serve any time.
Karla was 13 when Dally snatched her from Lower Hutt in 1989. He raped and tortured her before burying her alive. Dally has been in prison for 28 years, having been denied parole several times.
