Police have seized the financial records and interviewed key staff of a second charity linked to a former Government minister.
Roger McClay is being investigated for allegedly using his ex-MP perk of taxpayer-funded flights on business trips and then claiming driving mileage from the charity he headed.
Detectives executed search warrants on the Auckland home of the former National Party MP in June and seized financial records from Keep New Zealand Beautiful, of which he was the chairman.
Former staff and fellow board members have also been interviewed.
Police have also obtained the records of Heart Children New Zealand and detectives have spoken to senior staff members.
Lara Syddall, chief executive of Heart Children, confirmed that documents had been handed topolice.
She said Mr McClay worked as a contractor in a Government liaison role but declined to comment further.
Mr McClay performed a similar Government liaison and education role at World Vision.
Spokesman Phil Johnstone would not comment on whether the police had obtained World Vision records or spoken to staff.
Two other charitable trusts Mr McClay is involved with - Variety, the Children's Charity and For the Sake of Children - said they were not part of the police inquiry.
Mr McClay, 64, is under investigation for allegedly invoicing Keep New Zealand Beautiful for the cost of driving mileage, but taking a taxpayer-funded flight instead.
As a former MP, he is entitled to the 90 per cent subsidy for 12 domestic return flights each year.
No charges have been laid and he has denied any wrongdoing. He said he was disappointed at the length of the police inquiry but declined to comment further.
Mr McClay resigned as Keep NZ Beautiful chairman in July to take up a position at the NZ Spinal Trust.
During his time in Parliament, until 1996, he held positions as Minister of Youth Affairs and Associate Minister of Education and Social Welfare.
He was then appointed the Commissioner for Children and in 2005 was made a companion of the Queen's Service Order in recognition of his public service and contribution to the welfare of children.
A source said the Parliamentary Service, which administers the travel subsidies of MPs and former members of Parliament, spoke to staff at Keep NZ Beautiful last December before a complaint was laid with police.
The police inquiry was headed by Detective Senior Sergeant Greg Cramer, now a detective inspector on the North Shore.
A Parliamentary Service spokesman refused to comment on Mr McClay's travel claims.