Andrew "AJ" Freund, the 5-year-old Illinois boy allegedly killed by his parents, died from head trauma due to multiple blunt force injuries, according to the McHenry County coroner's office.
AJ's parents, Andrew "Drew" Freund Sr. and Joann Cunningham, allegedly forced the boy to stay in a cold shower "for an extended period of time" and may have "struck" him, according to court documents.
Both parents have been charged with his murder, police said.
AJ, of Crystal Lake, was reported missing on April 18, prompting a massive, week-long search. The deadly assault occurred on or about April 15, according to court documents.
AJ's parents ultimately provided information that led investigators to his body, Crystal Lake Police Chief Jim Black said at a news conference on Wednesday.
AJ's body was found on Wednesday in a shallow grave, wrapped in plastic, in a rural area near Woodstock, Illinois, Black said.
Cunningham, 35, was charged with five counts of first-degree murder; four counts of aggravated battery; two counts of aggravated domestic battery; and one count of failure to report a missing or child death.
Freund, 60, was charged with five counts of first-degree murder; two counts of aggravated battery; one count of aggravated domestic battery; two counts of concealment of homicidal death; and one count of failure to report a missing or child death.
Both are due to be arraigned on Monday.
During the search for AJ, his younger brother was placed in a different home under a Department of Children and Family Services (DCFS) safety plan, a DCFS spokesman told ABC News earlier this week.
DCFS has been in contact with AJ's family since AJ was born with opiates in his system in October 2013, DCFS officials said.
In November 2013, AJ was taken into protective custody and placed in foster care, DCFS officials said. AJ was returned to his home in June 2015, according to the agency.
In March 2018, DCFS officials investigated allegations of neglect by AJ's parents; the allegations were unfounded, according to DCFS.
The last contact between DCFS and the family was in December 2018, after Cunningham called the cops to report that AJ's father stole her cellphone and medication. Responding officers found a bruise on one of the children, but were "unable to make a determination of abuse," and released the kids back to the parents, according to police reports. Child protection staffers investigated the allegations of abuse and neglect, but the allegations were unfounded, a DCFS spokesman said.
The news of AJ's death is "heartbreaking," Marc Smith, acting director of Illinois DCFS, said in a statement Wednesday.
"Our priority is the care and safety of Andrew's younger sibling," Smith said. "The Department is committed to conducting a comprehensive review of the entirety of our work with Andrew's family to understand our shortcomings and to be fully transparent with the public on any steps we are taking to address the issues."
ABC News' Whitney Lloyd and Alex Perez contributed to this report.