Over the weekend, after a human foot was discovered, searchers recovered the head, two hands, and another foot of a child, according to the police department and the city's medical examiner's office. Investigators found the hands and feet in a lagoon in the park on Saturday and officers continued searching into the night, video footage from CNN affiliate WLS showed.

A source with knowledge of the investigation said it was a citizen who made the first discovery in the park.

A search of the same area Sunday recovered the head.

Chicago police spokesman Anthony Guglielmi said investigators also found a plastic bag that was brought to a lab to be opened in a sterile environment. Guglielmi said he believes the remains were somehow separated from the bag.

As search teams returned to the same area on Monday, the medical examiner's office said a pathologist would begin the examination process.

The park, which is centrally located near Chicago's New West Side, was closed. On Tuesday, investigators will continue scouring a lagoon in the park looking for more remains and evidence, according to the police spokesman.

There's still a lot that authorities don't know, though the fact the case involves a child is a challenge.

"Cases involving children are exceptionally difficult for all affected, even police," Guglielmi said on Twitter.

CNN's Greg Botelho and Seth Kovar contributed to this report.