"The investors were sold on a fantasy that purchasing these investment properties would successfully consolidate debt and solve their problems. Mr Cooper played on the affinity he had built with one family in particular. This has only added to their financial strife. Investors need to remain aware of their vulnerability in such situations," acting-SFO head Simon McArley said.
Cooper is due to be sentenced in March and is on bail.
Cooper was involved in the incident with Haiu in May 2011 after a property deal - not linked to the SFO charges - went sour.
Haiu was discharged without conviction at the Pukekohe District Court in August of that year after pleading guilty to assault.
The court heard how Haiu went to Cooper's house and punched the property developer twice in the face after the rugby player had lost $400,000 to $500,000 to Cooper.