Three detectives from the CIB in Auckland have now been assigned to investigate an incident involving broadcaster Tony Veitch and his former partner.
Mr Veitch has been stood down from his positions at Television New Zealand and The Radio Network, after reports that he broke four of the her vertebrae.
He is reported to have paid her $170,000 to keep the matter quiet.
A police spokesperson says the detectives have been working on the investigation for several days, but there is no timeframe for completion.
Police previously assigned one officer to investigate, after Mr Veitch publicly stated at a news conference that he "lashed out" at his former partner.