Dr Norman said he learned of Mr White's involvement only after other Green members recognised his voice in a radio interview early yesterday.
"At that point, because we knew that Mr White was the partner of my EA, we talked to her about it and found out what she knew."
Mr White was not an active member of the Greens, Dr Norman said, and while the networks used to co-ordinate the stickering were not Green Party ones, other Green Party members may have been involved.
Mr White told the Herald he didn't know whether others he worked with were Green Party members.
Dr Norman said the party may try to find out whether other members had been involved, but not until after the election.
"I really am focused on the campaign rather than getting involved in an investigation."
He had spoken to all of his MPs and "as far as we're aware none were involved". However, the party had not spoken to all of its candidates to ask about their involvement.
Dr Norman didn't believe the incident had damaged the Greens' relationship with National with whom his party wishes to strike another "memorandum of understanding" to advance green policies, if the John Key-led Government is returned next weekend.
It was up to voters whether the affair affected the Greens' support which is at historically high levels of above 10 per cent in recent polls.
"People know these kinds of things can happen in a large organisation and really the judge is how does the leadership of the organisation respond to it. I hope that people will see our response has been decisive and clear."
But Mana Party candidate and former Green Party MP Sue Bradford said she was shocked by the Greens' response and in previous times the party would have been proud of Mr White's actions.
"I feel quite sad in a way because I'm sure there were good Green activists that were part of this action and I'm sure they did it believing they were doing a good thing."
Condemning Mr White's actions "just shows how low the Green Party has sunk".
"You've got to ask how much of this is cuddling up to John Key and getting ready for what might happen after the election."
National Party campaign manager Steven Joyce confirmed he had accepted the Greens' offer of help to remove the stickers and work had already begun in some areas.
Appearing on TVNZ's Close Up last night, Mr White offered the Greens - but not National - an apology.
"I'm really sorry the Green Party feels that it reflects badly on them. I'm really sorry that this has gone so badly for my partner ... but in terms of the message we were trying to get out I don't have any regrets about that."
Mr Key said it was possible National would refer the matter to police but they had not been in touch with Mr White by last night.
However, the Electoral Commission has confirmed it is making an initial assessment as to whether the stickers, which did not carry a promoter's statement, breached election advertising rules.