In a message intended for the slain boy, the chief said, "We know you are at peace playing in heaven's playground and are happy you no longer have to suffer."
Black said his efforts are underway to confirm that the body is AJ's and that his department won't be releasing further details in an effort to protect the integrity of the ongoing investigation.
Officers removed several items from the family home, including a shovel, mattress, paper bags and a plastic storage tub.
Authorities said the couple reported AJ missing last Friday NZT and told officers they had last seen him at bedtime the previous night.
Early on in their investigation, though, police said they didn't believe the boy was abducted or that he had left the home on foot.
They also said they were "focusing on the residence and the individuals that may have seen or had contact with AJ last," and that Cunningham wasn't cooperating with detectives.
The department released more than 60 pages of police reports written by officers who responded to various calls about the house, which is about 72km northwest of Chicago.
One report described seeing the home littered with dog faeces and urine, and a children's bedroom where "the smell of faeces was overwhelming."
Another report said the officer found the house to be "cluttered, dirty and in disrepair," and without electrical power.
The heavily-redacted reports also indicate state child welfare workers were called after officers spotted a large bruise on one of the young boys living there, but that the children appeared to be "healthy and happy" and were not removed from the house.
Cunningham and Freund were in court seeking custody of their 4-year-old son, Parker.
Parker was taken into custody by the Illinois Department of Children and Family Services.
- AP
