The mother accused of beating and killing 5-year-old AJ Freund pleaded guilty Thursday morning to first-degree murder, leading prosecutors to file a 10-page document detailing the abuse the young boy suffered at his Crystal Lake home.

An unshackled JoAnn Cunningham appeared in McHenry County Circuit Court accompanied by a correctional officer as she entered a guilty plea to an amended count of first-degree murder. Prosecutors filed an updated version of the indictment in court Thursday, deleting the words “brutal” and “heinous” from one of the counts. Had the case gone to trial and jurors determined that AJ’s death was “accompanied by brutal and heinous circumstances,” Cunningham could have faced natural life in prison, McHenry County State’s Attorney Patrick Kenneally said.

Prosecutors plan to ask for the maximum 60-year sentence, which would ensure that 36-year-old Cunningham remained behind bars until she is 96 years old.

“I think that our primary goal is justice,” Kenneally said after the plea hearing Thursday. “This is the type of case where no matter what happens, you’re never ultimately going to be satisfied. But there’s a long way to go, not only in terms of Miss Cunningham’s sentencing, but also in terms of [AJ’s father, Andrew Freund Sr.]. ... There’s still a lot of work to do.”

The night of AJ’s death, Cunningham found soiled underwear the boy apparently had hidden in his closet. As punishment, Freund spanked AJ, and the parents placed the boy in a cold shower for about 20 minutes while Cunningham intermittently sprayed the boy in the face with a spray bottle, Freund told police. He ultimately suggested that AJ fell in the shower.

Had the case gone to trial, however, an expert witness would have testified that the head trauma and multiple blunt-force injuries AJ suffered were consistent with child abuse, not hypothermia or falling, prosecutors wrote in the 10-page factual basis to support Cunningham’s plea.

Cunningham’s attorneys, Assistant Public Defenders Richard Behof and Angelo Mourelatos declined to comment. The pair has ordered Cunningham a series of psychological evaluations, which they can potentially use in mitigation during sentencing.

The McHenry County State’s Attorney’s Office also would have presented evidence regarding prior abuse in the home. One of those instances was captured on a March 27 cellphone video during which a visibly bruised and scraped AJ reportedly threatened to get his mother “in trouble with someone.” At one point, Cunningham grabbed the young boy by the throat and choked him against the wall, according to prosecutors’ filing.

In the same video, AJ told Cunningham that he “just wants to be alone and not have anyone around him” and said “I just don’t want a family.” Cunningham replied by yelling, “You don’t have one ... that’s daddy included,” and went on to say, “‘You have daddy all mixed up. You really think daddy would choose you over me and [AJ’s younger brother].” Cunningham continued that Freund thought AJ was a “liar” and “manipulator,” prosecutors wrote. Cunningham allegedly told AJ that he thought he could do anything he wanted, then placed her mouth to AJ’s ear and screamed, “It doesn’t matter, it doesn’t matter (sic) none of it is gonna happen (AJ living alone with his father) ... ever.”

Cunningham entered her plea in almost a whisper Thursday. When asked if she would like to say anything further, she paused and Behof whispered in her ear before she said “not at this time, your honor.”

Cunningham entered what’s known as a blind plea, a plea without an agreement between a defense lawyer and prosecutor as to the sentence.

All of the remaining charges were dismissed in exchange for Cunningham inking the plea deal. The murder charge carries a penalty of 20 to 60 years in prison, which must be served in full. Additionally, Cunningham would have to register as a violent offender against youth.

Cunningham and Freund were arrested April 24 and charged with first-degree murder and a litany of other felonies tied to AJ’s death.

The pair made separate court appearances in a packed courtroom later that month when they pleaded not guilty to charges laid out in a 30-page grand jury indictment.

Both Cunningham, 36, and Freund, 60, previously requested trials by jury. It’s unknown how Cunningham’s plea might affect Freund’s case. She could be called to testify as a witness at Freund’s trial, although any potential cooperation was not a factor in her blind plea, prosecutors said.

Like Cunningham, Freund is accused of repeatedly striking AJ and forcing him to take “timeouts” for hours at a time between Sept. 20 and April 17, charging documents show. He also is charged with battering AJ on March 4 in relation to a separate video from that day on Cunningham’s phone. In it, Cunningham is heard “berating” a bandaged and severely bruised AJ, according to a police affidavit that has since been sealed.

Thursday’s court filing showed that Freund conducted a Google search on his cellphone about 3 a.m. April 15, typing in the search term, “child CPR.” Freund’s cellphone was searched after investigators obtained a search warrant to extract the data. Freund told police during his April 24 interview that AJ died at some point during the evening of April 14 after Cunningham “had engaged in ‘some hitting’ ” and placed AJ in the cold shower, prosecutors wrote. He allegedly told police that Cunningham awakened him at 3 a.m. April 15 and told Freund that AJ wasn’t breathing. He placed AJ’s body in a plastic tote in the basement and two days later buried the boy in a shallow grave outside of Woodstock, prosecutors said.

Freund’s next court date is scheduled for Dec. 13. Prosecutors have not offered him a plea deal, they said.

Cunningham and Freund both are being held in the McHenry County Jail each on a $5 million bond.

Since AJ’s death, the state’s attorney’s office has worked to improve communication between all the agencies that become involved in child abuse and neglect cases, officials said.

“We’ve had ongoing talks with [the Illinois Department of Children and Family Services] almost on a weekly basis,” Kenneally said. “We are in the process of revamping a lot of our protocols, and we’re also in the process of making sure that any type of alleged battery or sexual abuse of a child, that if there’s a police report generated, we get that police report for our own review.”

The office also has assigned special prosecutor and criminal supervisor Sharyl Eisenstein to oversee the McHenry County juvenile abuse and neglect courtroom.

• News Editor Kristen Zambo contributed to this report.