‘Flexing’ prison guard releases aggressive inmate before attack on coworker

A former Michigan corrections officer is facing a felony charge after prosecutors alleged that she intentionally opened the cell of an aggressive maximum-security inmate, allowing him to rush and attack one of her coworkers inside the Baraga Maximum Correctional Facility.

My UP News reporter Schyler Perkins said newly obtained body-camera footage and prison incident reports shed more light on the March 28 encounter involving former corrections officer Shelby Pennock, inmate Rickey Lee Martin and 23-year-old corrections employee Devin Deroche.

Pennock, 44, has been charged with assault of a prison employee under an aiding-and-abetting theory, although prosecutors are not accusing her of physically carrying out the attack herself. She has pleaded not guilty and has denied intentionally releasing Martin.

The case has drawn particular attention because an internal report says Pennock had earlier described a practice of opening the doors of threatening inmates to “flex” on them and show that they would back down when given the chance.

Body Camera Captured the Moments Before the Attack

Perkins reported that the attack happened in the prison’s segregation unit, where Deroche was walking through the block on his way to escort another inmate to a telehealth appointment.

Video obtained by My UP News shows Pennock standing near Martin’s cell while shouting can be heard from inside.

“Let’s go! Let’s go! Open this,” Martin can be heard yelling.

According to Perkins, Pennock then looked toward Deroche and said, “Ready?” before manipulating the cell door.

Nine seconds later, Martin came out of the cell and moved quickly toward Deroche.

Deroche told My UP News that he initially had little idea what was happening and was trying to understand the situation before the door suddenly opened.

“I was kind of observing a little bit, you know, and trying to figure out what the heck was going on,” he said. “And then, you know, all of a sudden, I hear the door crack open and see a prisoner coming out running towards me.”

The video is central to the prosecution’s theory because of the timing between Pennock’s remark and the door opening, but Pennock has maintained that the release was accidental.

Pennock Said the Door Opened by Mistake

After the incident, Pennock gave explanations that investigators later compared against the video and other prison records.

According to an incident report cited by Perkins, Pennock told investigators she had been concerned that the door was not secured and accidentally turned the key the wrong way.

“She said she opened the door accidentally,” the report states, adding that Pennock said turning the key one direction opens the door while the other direction closes it.

Deroche said Pennock also told him she had been trying to deal with a towel that was caught in the door.

Prison officials later noted that her explanation had shifted between a piece of paper and a towel being stuck in the doorway.

Pennock continued denying that she had deliberately set up an attack, and body-camera footage from her arrest shows her questioning why she would intentionally release the inmate if she was then going to help intervene.

“You know, they’re making it seem like I intentionally let him out,” she told an arresting officer. “And if that was the case, why would I have gone? You’d think I’d run the other way. I wouldn’t help.”

That is an important part of the case because the footage may look suspicious, but intent remains the central disputed issue, and Pennock has not been convicted.

Inspector Says Earlier Recording Mentioned ‘Flexing’

The most damaging allegation may come from what prison inspector Pynnonen told investigators about Pennock’s own body camera from roughly two hours before the assault.

Perkins reported that Pennock had removed the camera and placed it in a drawer, but the device continued recording audio.

According to the incident report, Pynnonen said Pennock could be heard describing how she dealt with inmates who acted tough by opening their cell doors and challenging them, something he described as “flexing.”

The report says Pennock stated that when she opened the doors of inmates making threats, they usually backed down.

Pynnonen told investigators that he believed Pennock was doing something similar when Martin’s door opened, and he said she had at times acknowledged “flexing” during an internal hearing before returning to the explanation that something had been caught in the door.

That earlier recording does not by itself prove what Pennock intended during the later incident, but it gives prosecutors a piece of context they can use to argue that the cell opening was not simply an accidental turn of a key.

It also raises serious questions about judgment inside a maximum-security facility, where deliberately testing whether an agitated inmate will act on a threat could expose staff members and other prisoners to obvious danger.

Weapon Found Inside Martin’s Cell

Martin was not just an upset inmate making verbal threats.

Perkins reported that after the assault, staff searched his cell and found what Deroche described as a makeshift shank.

Michigan Department of Corrections records identify Martin as a Level V maximum-security inmate who was originally sent to prison for fleeing police.

Deroche later said the situation could have ended much worse than it did.

“It could have been a really bad day, but thankfully it wasn’t,” he said.

That discovery adds another layer to the seriousness of the incident, because if Martin had managed to reach the weapon before or during the confrontation, the attack could have escalated beyond what was captured on camera.

The presence of the shank also strengthens the argument that opening a cell during an angry confrontation carries risks that go well beyond a verbal show of force.

Pennock Defended Her Actions After Arrest

My UP News also obtained body-camera footage from Pennock’s arrest, where she continued trying to explain that she had not intentionally caused the attack.

At one point, she suggested inmates inside the prison can be manipulative and difficult to read.

“These guys are pretty slick in there while they operate,” she told a state trooper.

The trooper responded that those issues were matters she would need to discuss with an attorney.

After arriving at the police station, Pennock again said she was upset because she had not intended for the incident to happen.

Her defense appears likely to focus on accident and lack of intent, while prosecutors are pointing to the timing of the door opening, the “ready?” remark and the earlier recorded discussion about opening cell doors to challenge aggressive inmates.

The case will ultimately turn on how a court interprets that evidence.

Felony Charge Could Carry Five Years

Pennock was arraigned in July on one count of assault of a prison employee, a felony punishable by up to five years in prison and a $2,500 fine.

She was released on a $500 bond and is scheduled to return to court for a pretrial hearing in November.

The charging document alleges that she aided and abetted Martin in the assault on Deroche, though Perkins noted that it does not spell out every detail of how prosecutors say she did so.

That leaves the video and internal prison reports especially important as the case moves forward.

For Deroche, the incident remains troubling because he believes the circumstances made the attack feel less like a random accident and more like something that may have been allowed to happen.

“I couldn’t help to think that it was almost done on purpose, just because of the circumstances,” he told My UP News.

At this stage, that remains an allegation rather than a proven fact.

Still, the combination of the footage, Pennock’s earlier recorded comments about “flexing” on inmates, and the later discovery of a weapon in Martin’s cell has turned what might otherwise have been treated as an internal prison mistake into a criminal case that now carries the possibility of years behind bars.