The ABC7 I-Team has examined so-called "digital forensics" that could have pinpointed suburban cell towers where the parents' phones were before AJ was first reported missing.
RELATED: Parents of AJ Freund charged with murder after boy's body found
This is the backstory of how police and the FBI leveraged that information during interviews with the boy's parents.
It started at sunrise with the FBI's mobile forensics truck and a swarm of law enforcement at a farm field in Woodstock.
The question was: why were they converged eight miles from the boy's home?
WATCH: Evidence collected from Crystal Lake home of missing boy
The answer came a few hours later, when charges were announced against the boy's parents.
"During the overnight hours, investigators with the Crystal Lake Police Department and the FBI interviewed both Joann Cunningham and Andrew 'Drew' Freund Sr. after information was obtained through a forensic analysis of cell phone data," said Crystal Lake Police Chief James Black.
Confronted with that cell phone data in the early morning hours, investigators say AJ's parents provided information that pointed police to the shallow grave containing the remains of their son.
RELATED: Crystal Lake mourns 5-year-old boy after body found, parents charged with murder
Since the late 1990s, law enforcement-and private investigative businesses have done forensic exams of cell phones to track people and identify their proximity to crimes, accidents and wrongdoing.
"It can be very powerful evidence and as happened here, it looks as if it was used to extract an admission or a confession that led the police to the body," said ABC7 Legal Analyst Gil Soffer, a former federal prosecutor. "Without this kind of evidence, all the police would be able to do is to look at someone and say, 'Now just tell us the truth, where were you and what were you doing?' That doesn't get you very far."
Wednesday night, the suspects were in jail facing a total of 23 felonies, including five counts each of first-degree murder.
TIMELINE: DCFS interaction with AJ Freund's family
"There are different ways to commit first-degree murder under Illinois law," Soffer said. "The state can offer different theories for first-degree murder and if the evidence supports any of those theories, you have a conviction. So it really is the state covering their bases and making sure they're putting all viable theories for a jury to consider someday."
With the charging paperwork in this case not expected to be filed until Thursday morning, and authorities not explaining how they arrived at the slew of charges against the parents, it is difficult to tell exactly how the case will be prosecuted. Our legal expert Gil Soffer said it appears both AJ's mother and father are charged as equally culpable in the killing of the little boy.