Last week’s case of malfeasance and lax supervision of inmates on “work lines” by city parks supervisors — inmates who ended a brief work shift with an extended swim at a public beach — is wrong on so many levels it surely makes any rational person’s head spin.

Four city park labor supervisors on Friday were put, appropriately enough, on unpaid leave while the criminal case is investigated.

The charges, still pending, involve drugs and contraband, but it’s the brazen nature of the  lapse that makes all this so egregious: The public must not accept anything less than an aggressive investigation.

Further, the state and city owe taxpayers evidence that there’s been a crackdown on the prisoner work lines program and that such a failure of correct public-safety protocols hasn’t become commonplace.

Let’s review the allegations. All 12 arrests stemmed from an attempt to slip contraband and illegal items — tobacco, a substance appearing to be crystal methamphetamine, and a pipe for ingesting the “ice” — onto the grounds of the Oahu Community Correctional Center.

The eight arrested inmates were in the van that, upon inspection at the gate, was found to contain the drug paraphernalia and the suspected drug.  The other three vans in the case contained other inmates, who were not arrested, and loose tobacco as well as cigarettes — items often used for bartering inside the prison.

This discovery followed an anonymous tip earlier in the week that prisoners were swimming at Magic Island. City officials had been instructed specifically not to take inmates on work crews to the beach, said Jodie Maesaka-Hirata, the state’s public safety director. None of the four work crews involved had any work scheduled at Magic Island, officials said.

Worse, the stop at the beach was not a brief respite at all, but instead exposed the public to a security risk for three hours at a time, allegedly on two separate occasions last week.

Employing inmates in public facility projects ought to be a valuable aspect of the rehabilitative program and a service to community besides. However, the notion of working for three hours and swimming for three falls far short of that standard and seems less defensible as a means of instilling a work ethic. Many of us would love to have such an easy work schedule.

It’s logical to wonder how often this had been going on before it was reported. And the fact that one of the four city supervisors is the brother of the city parks director ought to underscore the need for the fullest cooperation with investigators, something that the Carlisle administration has pledged to do.

Maesaka-Hirata, who supervised the Public Safety Department’s work line program for six years, trained three of the four city employees for this duty. They knew the rules and must be held fully accountable, fired from their jobs if the case is proven.

It’s a “wake-up call” to others who underwent similar training, she said, but that’s an understatement. More than simply being awakened, everyone in the program should be subjected to tighter controls, effective immediately.

This whole episode has been an embarrassment to city and state agencies involved. Another one like it would be simply intolerable.