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Villanueva said surveillance video captured last month at the Pitchess Detention Center in Castaic shows inmates huddled in a common area drinking from the same container and passing around a mask in an attempt to elevate their temperatures, he said in a virtual press conference.
It was unclear if any of the inmates had the virus.
“It is dismaying to realize anyone would intentionally infect themselves,” Villanueva said. "There's a reason these people are behind bars to begin with because they violated the norms of society."
A nurse took the temperature of the inmates, who used the hot water to create COVID-19 symptoms, the sheriff said. Within a week of the video being taken, 21 inmates tested positive for the virus.
“We had zero positives up until that spike, but that now, also, that has impacted our staffing as well," Villanueva said.
The inmates denied trying to infect themselves when questioned by investigators, he said.
Officials said an inmate trustee discovered the plot after finding items his fellow prisoners believed would infect them with the disease. The trustee was beaten by other prisoners after he tried to disrupt the scheme, officials told the Los Angeles Times.
The county has reduced its jail population in the face of the coronavirus crisis. Officials have reported 357 confirmed cases in the Los Angeles jail system, the nation's largest. As of Friday, the jails held more than 11,000 inmates in a system that typically houses around 17,000, Villanueva said.
Many of those released had less than 30 days remaining on their sentences. Had the jail facilities had per-pandemic populations, the results would have been "catastrophic," Villanueva said.