In Adelaide Magistrates Court, David Barry Hawkins, 38, has admitted abusing his position between January and February 2008 at Port Pirie.
A private investigator, Heath Lee Boyle, 34, has pleaded not guilty to 26 counts of aiding and abetting Hawkins in the improper use of his office.
Another former police officer, Paul Andrew Simmonds, 46, also is facing a count of abusing a public office to secure a benefit.
The arrests stemmed from an investigation by the police anti-corruption branch.
Hawkins and Boyle will face the Adelaide District Court next month, while Simmonds will return to Adelaide Magistrates Court later this month to enter a plea.