The lessons to be learned from the Honolulu Police Department corruption scandal have only begun to tumble out, with last week’s indictments of Louis Kealoha, the retired police chief, along with his wife, city Deputy Prosecutor Katherine Kealoha.

This much seemed evident from the start: Unchecked secrecy in a law enforcement agency is a dangerous thing. Lack of disclosure, critics have said, is what would allow a police chief to deploy investigators in pursuit of personal interests, rather than serving the public.

That is what Louis Kealoha is accused of doing.

HPD’s elite Criminal Intelligence Unit (CIU), with personnel hand-picked by the chief, was formed in the late 1970s to investigate terrorism and organized crime. In this case, individuals serving within CIU are alleged to have played a part in a scheme to frame Katherine Kealoha’s uncle, Gerard Puana, for the theft of documents. This was pursued as a way of blunting Puana’s civil complaint that the Kealohas had misappropriated family funds. The operation, investigated by the FBI, led to the indictment of CIU officers as well.

Regardless of how the prosecution ends up, there must be more immediate action taken to strengthen the integrity of the CIU. There are some who argue that a secret and specialized force, under the sole supervision of the chief, should be disbanded.

But some advocates for greater transparency, including former lawmaker and police officer Annelle Amaral, argue more persuasively that a covert squad does serve a purpose. In gathering intelligence on specific and complex criminal matters, it is rational to tightly control knowledge of operations. Spread the information too broadly, and there is greater risk of leaks, and of a blown cover.

That doesn’t mean the police chief alone should hold the reins. Amaral also argues that oversight should be provided by an agency outside HPD but within the law enforcement community so that the intelligence gathering still can be protected.

Whether this is a component of another agency such as the FBI or a special group of professionals convened for the purpose is something the Honolulu Police Commission, as well as the mayor, should discuss.

This would be a long-overdue action aimed at improving the accountability of intelligence gathering. The overseers should demand a clear understanding of what the intelligence unit is doing from the police.

And then the police commission, which serves as the representatives of the general public, must mandate a regular report from the oversight providers.

Even if that feedback contains information redacted to protect an ongoing investigation, the feedback requirement should serve as a deterrent against unauthorized activity that could run afoul of the law. This becomes exceptionally important, as the CIU has no clear mandate or rules.

Certainly, HPD already knows how the ongoing Kealoha case has compromised public trust in department practices, and has moved to make some changes.

Cary Okimoto, the acting HPD chief who is retiring at the end of November, said he meets every other day with the unit’s officers to learn what they’re doing. That’s still not optimal. An external set of eyes on this unit is what’s required.

Additionally, CIU, which comprises 19 officers, went through an overhaul as the controversy unfolded, officials said; most officers now part of the unit enlisted after the Puana mailbox episode.

Eric Seitz, who represents Puana in a lawsuit against the city, said problems with intelligence gathering have sparked lawsuits in Chicago, Los Angeles and New York. It would be wise to improve oversight to keep Honolulu off that list of cities.

Indeed, the risk presented by an investigative fiefdom, wholly controlled by a police department’s chief, is what’s playing out in the headlines now.