The OPI raided the squad's offices in a Melbourne suburb yesterday seizing paper and electronic documents.
OPI assistant director Graham Ashton said the raid is part of a four-month investigation based on complaints concerning the methods used by some squad members.
If the allegations proved correct, the armed offenders squad should be disbanded and some members charged.
Five years ago, Victoria's police drug squad had been already disbanded and reformed following an anti-corruption investigation in 1992.