Veitch pleaded guilty in the Auckland District Court in April to assaulting former partner Kristin Dunne-Powell with reckless disregard for her safety.
He was fined $10,000, ordered to do 300 hours community work, and placed on supervision for nine months.
His lawyer, Stuart Grieve, QC, complained to the Independent Police Conduct Authority (IPCA) over the involvement of Detective Keitha Lally in the case, alleging she had a conflict of interest.
As a result the IPCA has criticised Ms Lally's involvement in the criminal proceedings.
Ms Lally and Ms Dunne-Powell attended the same gym class, and the latter spoke to Ms Lally before laying an assault complaint with police. The detective then worked on the case, including interviewing witnesses and getting medical records, and was present when Veitch was arrested.
Police National Headquarters Assistant Commissioner (Operations) Viv Rickard said police had "promulgated a policy on safe processes for the independence of investigations". The policy followed a Commission of Inquiry, set up to investigate police behaviour following rape allegations by former Rotorua woman Louise Nicholas and Kaitaia's Louise Garrett.
"This includes the requirement to immediately declare any potential or perceived conflict of interest," Mr Rickard said.
He acknowledged the IPCA had issued some "criticism related to some aspects of potential or perceived conflicts of interest in the case".
Mr Rickard said that other actions complained of by Mr Grieve were found by IPCA head Justice Lowell Goddard to "not only to comply with police practice, but were reasonable in the circumstances and justified".
The IPCA findings had been distributed to all police staff.
"This was a high-profile case which attracted considerable media interest because of the parties involved before our investigation even started," Mr Rickard said.
"We will take on board the experiences from this case, our own debrief into the investigation, and the IPCA's comments to help us shape the management of future high profile investigations and operations."
