DARTMOUTH, Mass. (WPRI) — The inmates who carried out a destructive standoff last week at a Dartmouth jail had planned it the night before, according to Bristol County Sheriff Paul Heroux.

Heroux said the correctional officers were trying to move inmates to a different cellblock on Friday when more than a dozen so-called “ringleaders” refused to comply. Those ringleaders then riled up their fellow inmates, leading to the six-hour standoff.

The inmates caused hundreds of thousands of dollars’ worth of damage before correctional officers took back the housing unit, according to Heroux.

“They had already started talking amongst themselves the night before to push back,” Heroux said. “They didn’t want to change housing units because they knew where they were going was going to be a housing unit that was going to have locked doors.”

WATCH: Heroux gives details, shows photos of damages after standoff (Story continues below.)

Heroux said correctional officers were shuffling inmates around so their cells could be modified as part of his overarching plan to reduce the risk of suicides and close the controversial Ash Street jail.

The modifications include installing toilets in cells, adding locks on doors and installing suicide-resistant bed frames. Heroux said that nearly 50% of the prison’s cells don’t have toilets inside, meaning the doors can’t legally be locked.

“Some inmates got it in their heads that they wanted to stay right where they were, and it doesn’t work like that,” Heroux explained.

Heroux said making the prison more “suicide-resistant” will protect inmates from themselves, adding that the uncertainty of being imprisoned can make some more susceptible to taking their own lives.

“They’ve never been arrested before, it’s a serious charge … these are risk factors for suicide,” he said. “They think their life is over.”

Heroux released more than three dozen images showing the aftermath of the standoff. He also plans on releasing video footage of the incident at some point.

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The images show mattresses being used to barricade entrances, broken windows and debris strewn around the housing unit. Wires and lighting fixtures were also ripped off the walls.

“I wouldn’t call this a riot though,” Heroux added. “A riot by definition is violent. There was really no violence. This was destructive, but it wasn’t violent. Nobody got hurt.”

Heroux said when the standoff began, correctional officers acted quickly by deactivating the prison control panel and exiting the housing unit. He credited their actions with stopping inmates from getting out into the courtyard and preventing it from becoming a hostage situation.

“They were seconds away from being locked in there with the inmates, which would have been a hostage situation,” Heroux said. “It was really that close.”

Heroux said the officers had a “show” of force, but claims it never had to be used.

Correctional officers decided against using dogs to control the situation to avoid the perception of them being used to bite inmates and prevent their barking from making matters worse, according to Heroux.

“The dogs aren’t doing anything other than being a distraction, making noise, and we wanted to make sure we were calm,” Heroux said. “The dogs wouldn’t help. That would only escalate the situation.”

Officers attempted to rein in the situation by negotiating with inmates through windows, but it reached what Heroux called a “point of no return” as they tried to “reason with unreasonable people.”

“We showed force by using gas and flashbangs, and that disoriented the inmates so that [correctional officers] could enter and get past the barricades,” Heroux added. “But once inside, the inmates basically succumbed to and they got down, they were handcuffed, they were brought out one by one.”

The inmates handed over a list of demands during the standoff, which included installing televisions in cells and lowering canteen prices. Heroux sent a letter in response, which he said was immediately torn up and thrown out the window.

“Some of the demands were to speak to me right away,” Heroux said. “That wasn’t going to happen. That probably would have escalated it even more.”

Heroux said 20 inmates will likely be charged in connection with the standoff, though it’s unclear what those charges will be. The so-called ringleaders have since been separated and transferred to other jails, while the remaining inmates were moved as originally planned.

Sarah Doiron and Elizabeth Turley contributed to this report.