Mark Bowen, warden of the Northeast New Mexico Detention Facility in Clayton, received a note in September 2017 warning that a convicted serial killer serving a nearly 200-year sentence in the prison was planning to harm his staff, according to an email he issued to a handful of workers.

The email, which surfaced recently, warned of the potential threat posed by Clifton Bloomfield — who pleaded guilty more than a decade ago to killing five people in Albuquerque. Bowen ordered staff to “ensure that all precautions are used when dealing with this inmate.”

That meant a guard must be accompanied by a supervisor, and a surveillance camera must be operating at the time, the email said.

Less than two weeks later, however, Bloomfield convinced a rookie corrections officer working alone at night in the inmate’s cellblock to open his cell door. Reports say Bloomfield assaulted the guard, escaped with his keys, freed several other prisoners and then incited an hourlong uprising in which one inmate was nearly killed and another alleged he was raped.

State prosecutors have portrayed the young guard, Matthew Shriner, as both a victim and a culprit in the Sept. 23, 2017, riot. A criminal case against Bloomfield accuses the inmate of holding Shriner hostage and assaulting him before starting the riot. But Shriner also faces felony counts, charging him with “intentionally” permitting Bloomfield to escape custody, unlawful rescue of a convicted capital offender and assisting in an escape.

Bowen’s email directing staff to follow strict procedures when tending to Bloomfield raises questions about why Shriner, an inexperienced guard, was working alone in the prisoner’s cellblock that night and who should be held culpable for the riot.

Shriner, who was 22 at the time of the riot, has filed a lawsuit accusing the New Mexico Corrections Department and private prison operator GEO Group of forcing him to work solo in a cellblock where “the most hardened dangerous criminals” are held, even though he was “uncertified, not properly trained, and inexperienced in corrections security.”

He also was sick and exhausted from being overworked at the severely understaffed prison, he said in the complaint, filed last year in state District Court.

According to a KRQE-TV report, the riot erupted on a night when only nine of what should have been 20 corrections officers were on duty.

Shriner’s lawsuit said he was “scapegoated” for the riot and placed on unpaid leave.

He declined to comment on the case this week, saying his lawyer advised him not to speak about it because of the criminal charges he’s facing.

His attorney, Mark A. Earnest, also declined to comment, saying he expects the case to go to trial.

Eighth Judicial District Attorney Donald Gallegos — who has announced he’ll retire at the end of the month with more than a year to go on his term — did not respond to a request for comment from his office on the charges against Shriner.

In his email issued Sept. 12, 2017, Bowen wrote: “We received a kite [note] this morning stating that inmate Bloomfield who is housed in [Restrictive Housing Unit] wants to harm our staff. All of us know how dangerous this inmate is. … Ensure a supervisor and camera is present when his food tray slot or cell door is open.”

A paper copy of the email was provided to The New Mexican anonymously, and Gov. Michelle Lujan Grisham’s office has confirmed it was authentic and that Bowen sent it to staff that day.

Just 11 days later, Bloomfield “tricked” Shriner to open the door to his cell, the former guard said in his lawsuit.

According to an internal review of the riot included with the suit, Bloomfield held a weapon fashioned from a toothbrush against Shriner’s throat and ordered the guard to give him the keys to neighboring cells.

Shriner, “by some miracle, disengaged from the headlock and grasp of Clifton Bloomfield, jumped over a railing onto a concrete floor, sustaining severe injuries to his body, escaped and summoned help,” according to his lawsuit.

Bloomfield, meanwhile, proceeded to release other inmates, who collectively took control of the unit for more than an hour before corrections officers subdued them with tear gas, flooding and flash grenades, the internal review said.

During the melee, the document said, one inmate had his throat cut and was airlifted to a nearby hospital; another inmate reported he was raped during the incident.

Tripp Stelnicki, a spokesman for Lujan Grisham, referred questions about Bowen’s directive on Bloomfield and whether prison officials could have prevented the riot to either Bowen or his employer, the GEO Group.

But, Stelnicki said in an email, “The state’s procedure is two-person escorts in and out of restricting housing units, always. So if what you describe is what happened, we would be extremely concerned about that as it would represent a violation of procedure to which state expects its contractors to adhere.”

Bowen said Tuesday he couldn’t comment and referred questions to GEO.

GEO spokesman James Hallinan, in an email Tuesday, blamed the state for the riot.

“The previous administration should have never placed such a high-security inmate in a medium security facility,” Hallinan said. “… While we value our partnership with the state, we dispute certain findings within the previous administration’s New Mexico [Corrections Department] incident report related to staffing concerns, post assignments, and security measures, as well as specific findings related to the timeline of the incident.”

Hallinan said he was referring to the administration of former Gov. Susana Martinez, who was in office at the time of the riot.

Florida-based GEO has run the Clayton detention center for the past decade but announced recently it would not renew its contract with the state and the town of Clayton, which owns the facility. The company cited the difficulty it faced in keeping the facility adequately staffed.

While there are 204 allocated positions at the facility, a spokeswoman for the governor said, the prison had a staff of only 120 in late June, when GEO announced it was ending its contract. The state plans to take over operations during a three-month transitional phase beginning Aug. 3.

GEO still manages state prisons in Guadalupe and Lea counties.

Asked if Bowen will retain his position as warden at the Clayton prison when the state takes over management next month, Stelnicki said: “The current warden is free to apply for the job with the state like anyone else who is interested in the post.”