The comment from Sir Arnold came as Commissioner Gari Baki suspended anti-fraud detectives who had been investigating a major fraud case implicating the prime minister Peter O'Neill.
After being the subject of a stay order since 2014, the investigation resumed two weeks ago, prompting the arrests of the prime minister's lawyer, the attorney-general and a Supreme Court judge last week.
Baki had accused the suspended fraud squad officers of insubordination and circumventing police procedures by not keeping him informed of the fraud case.
After being appointed last year, the Commissioner tried unsuccessfully to derail the investigation, however Sir Arnold said his reasoning was flawed.
"Fraud squad officers, detectives, criminal investigators are all mandated under the constitution and laws to continue their investigations. They don't need to get the commissioner's signature and authority in every instance of their investigation. That's flawed. This is simply because this commissioner has been appointed by this prime minister and they are trying to corrupt the process."
Sir Arnold said the fraud squad officers had gone to court and the court had continuously upheld their responsibility and due process.