SAN JOSE — The three guards at Santa Clara County Main Jail were only supposed to be conducting a routine search of Michael Tyree’s cell, looking for extra clothing or toiletries that inmates often try to hoard. Instead, the correctional officers did something “violent and cowardly,” Sheriff Laurie Smith said Thursday, that left the 31-year-old mentally ill man lying naked on the floor, covered in lacerations and bruises and bleeding to death internally.

During a news conference Thursday, flanked by 18 uniformed members of her command staff, Smith announced the arrest of the three correctional officers on suspicion of murder, just a week after Tyree’s severely beaten body was found in jail wing 6B.

“The disappointment and disgust I feel cannot be overstated,” she said. “His life had value.”

The murder allegations against correctional officers 28-year-old Jereh Lubrin, and 27-year-olds Matthew Farris and Rafael Rodriguez, unprecedented in the 165-year history of the Sheriff’s Office, have put the jail it runs under a harsh spotlight and drawn attention to the difficult plight and placement of the mentally ill.

Smith said she spoke privately with Tyree’s family, just hours after the arrests.

“I want to express my profound sorrow over the loss of Mr. Tyree,” Smith said, accusing her officers of losing their “moral compass.”

“This violent and cowardly act that took Mr. Tyree’s life is not indicative of the values we expect and honor with the men and women of this department.”

Rodriguez was arrested at his home in San Jose and Farris at his Campbell home, both around 5:30 a.m. Thursday. Lubrin turned himself in. They were stripped of their badges and put on unpaid leave.

Smith said the officers declined to give statements to investigators from the Sheriff’s Office, invoked their Fifth Amendment rights against self-incrimination and requested attorneys. While the officers work under the Sheriff’s Office, they are restricted to jail duties with limited authority outside its walls, and are represented by a separate union.

Santa Clara County Correctional Peace Officers’ Association President Lance Scimeca declined to comment on the case.

The three were booked on suspicion of murder, assault under color of authority, and conspiracy. A source familiar with the investigation said they were transferred to protective custody at a jail facility in Alameda County. Out-of-county holding is typical for suspects who work in jails or have sensitive law-enforcement assignments.

When he died, Tyree was similarly being held on the sixth floor of the Main Jail on West Hedding Street for a probation violation stemming from a minor drug-related arrest from a year ago. He agreed to enter a residential treatment program for substance abuse and was waiting for a slot to open up so he could be transferred to a facility.

“Our client was slated to be released to a mental health bed but no bed was available, thus the reason he was still in jail,” Santa Clara County public defender Molly O’Neal said Thursday. “This tragedy underscores the need for a greater number of mental health beds so that clients with acute mental health needs do not sit in custodial facilities which are not therapeutic when they have been ordered released.”

The sheriff announced that the FBI is looking into Tyree’s death at her request and that she has given the agency full access and welcomes their assessment. However, it appears based on interviews that the FBI was first called by the mother of an inmate, who was housed in a cell near Tyree and witnessed the guards entering his cell and then heard him screaming for help.

In a highly unusual sign of cooperation, the sheriff yielded the podium in the assembly room of her own agency to Paula Canny, the attorney representing Tyree’s family, who may well sue the county. Canny noted the tragic irony of what had been a consensus decision among law enforcement, social workers and Tyree’s own representative to keep him in custody until he could be moved to a mental facility.

“Everyone believed he was safer in a jail than to be released on the streets,” she said.

“The family and friends of Michael Tyree are heartbroken by the cause of Michael’s death. They are grateful for the efforts of Santa Clara County Sheriff Laurie Smith and her command staff to swiftly bring to justice the rogue correctional officers who, so sadly, betrayed their oath to protect and serve,” Canny said.

Under state law, the District Attorney’s Office has until Tuesday to file charges against the three officers.

Smith said that the night of Aug. 26, Lubrin and Farris were conducting a routine clothing search of inmates’ cells, and were joined by Rodriguez. During the search, inmates were locked in their cells and the three officers were the only jail staff in the wing.

Tyree was in a single-person cell when he was searched, Smith said. After about 20 minutes, the three officers left the wing, and no one else entered.

An hour later, into the early morning of Aug. 27, Lubrin re-entered the wing to conduct a routine welfare check and soon after issued a “man down” call on his radio after reportedly discovering the 5-foot-11, 150-pound Tyree on his cell floor naked, covered in feces and vomit, and unresponsive.

Smith said Rodriguez helped Lubrin pull Tyree out of the cell and perform CPR. Medical personnel soon followed, but they pronounced him dead about 12:35 a.m.

That was the entirety of the official narrative, and there is no known video of the interaction inside the cell. But several inmates who were also housed in the 6th floor wing reported seeing the three correctional officers go into his cell and then hearing him scream, “don’t,” “please, stop,” “help,” and “I’m sorry,” before falling silent after the officers left, according to a relative of one of the inmates.

It was only after Tyree’s body was discovered that the officers reported they used force to restrain Tyree because he refused to take his medication, according to a source familiar with the investigation. That was a breach of protocol, which requires that officers must immediately report any use of force and request medical care for the inmate.

At the Thursday news conference, county medical examiner Dr. Joseph O’Hara said Tyree suffered multiple blunt force injuries, including severe cuts to his liver and spleen.

“In short, he bled to death internally,” O’Hara said, ruling the death a homicide.

Smith made no mention of the correctional officers’ purported claim that they were trying to make Tyree take his medication. Even taken at face value, that would have also been a violation of protocol. Officers can physically compel an inmate to take his medication, but such interventions are expected to proceed in stages, and require a doctor’s approval, with a nurse administering the medication while officers hold the inmate down.

O’Neal, the public defender, criticized the officers’ conduct, noting the relatively short time they had been on the job.

“Having three very young, inexperienced C.O.’s dealing with clients like these is ill-advised,” she said. “Ideally, you’d have young C.O.’. s work with a senior C.O. and all of them would have training in dealing with mentally ill inmates.”

Canny dismissed the idea that more experience or better guard training could have prevented Tyree’s death.

“How much training does it take not to beat someone to death whether he was being given medication or not?” Canny asked. A source said Lubrin had at least two force complaints filed against him, one of them made recently.

Tyree’s death has elicited outcry from community groups, evoking parallels to the April in-custody death of Freddie Gray in Baltimore that sparked widespread civil unrest and charges against six police officers tasked with transporting Gray.

Raj Jayadev of the social-justice collective Silicon Valley De-Bug said a broad investigation of the jails and the officers working there is needed.

“Logic would dictate that there very well could be other incidents,” he said, “and it would be negligent on behalf of the county to not do a full, comprehensive investigation of our entire jail system.”

Staff writers Eric Kurhi and Katie Nelson contributed to this report.