(KTVU) Redwood City - San Mateo County Sheriff's Deputy Blake Lycett is now a criminal defendant, accused of beating three suspects at the County Jail in Redwood City.
The investigation began back in August, when one of the inmates came forward.
"An inmate, after being released, informed us that he was physically assaulted by one of the staff members at Maguire Correctional Facility," said Det. Rosemerry Blankswade, sheriff's spokeswoman.
The sheriff's office launched an internal investigation and realized it wasn't an isolated incident.
"We found out that there were two other possible victims involved," Blankswade said.
Prosecutors have charged Lycett, 42, with three misdemeanor counts of assault under color of authority.
The alleged victims are Luis Cardenas, Milan Jackson and Zephaniah Coon. Authorities say all were attacked by Lycett last August.
"Two of them who were going through the booking process, and one of whom was just an inmate where he punched them, kneed them and, on the last occasion, took the inmate and shoved him - his head - into a closed elevator door," said District Attorney Steve Wagstaffe.
Authorities say all three were resisting in some way, whether it was spitting at deputies or going limp. But investigators say that didn't justify being attacked by the deputy.
"Anytime anyone comes into our facilities, it's still our job to protect them," Blankswade said. "And whether it is from another inmate or staff, we need to make sure that their health and well-being is upheld."
The case was built on statements by the inmates, other jail staff "and, most importantly, on the surveillance system that the San Mateo County Sheriff's Office installed in our jail just within the last year or so," Wagstaffe said.
The deputy is on paid administrative leave. He's been with the sheriff's office for six years and previously worked as a Daly City police officer.
"Anytime we hear of these type of allegations it's obviously very disappointing and concerning, and they're taken very seriously," Blankswade said. "We're thankful for the inmates who had the courage to step forward."
Lycett and his attorney did not return calls requesting comment Friday. He is due in court next month to enter a plea.