By Holly Yan and Faith Karimi, CNN

(CNN) -- In his five short years, Andrew "AJ" Freund endured more trauma than any child should.

A home that reeked of feces and urine. Frequent visits from police officers and child welfare workers. A family life so unstable that he bounced from one caretaker to another.

Now the young boy is dead, found wrapped in plastic in a shallow grave. His parents are charged with murder. And those who knew about the family's troubles are left wondering whether they could have done anything differently to help prevent AJ's death.

A lifetime of problems

Soon after AJ was born, the Illinois Department of Children and Family Services got involved, spokesman Jassen Strokosch said.

The baby "was brought into care with us" when "neglect was indicated on part of the mom," Strokosch said.

So from 2013 to 2015, AJ was "in care with someone else," Strokosch said.

But the boy eventually returned home to his parents.

Last year, child welfare services were called twice to the family home: once for allegations of neglect in March, and once for allegations of abuse and neglect in December.

The allegations were determined to be unfounded in both cases, Strokosch said.

Now the Department of Children and Family Services will review its work with AJ's family to see if there were any shortcomings, acting director Marc Smith said.

If there are, the agency will tell the public what steps it will take to fix them, Smith said.

AJ's younger sibling was in the home until this week, but is now living with another family, Strokosch said.

"Protecting vulnerable children who come to our attention is at the core of our mission at DCFS," Smith said. "All of us feel this loss. Our priority is the care and safety of Andrew's younger sibling."

Police found ghastly conditions in the home

Child welfare services weren't the only ones streaming in and out of AJ's life. Crystal Lake police officers visited, too.

Last year, a neighbor in the Chicago suburb called police to check on the children because the home had been without power for weeks, according to a police report.

At the time, an officer wrote that two children appeared "healthy and happy." And child welfare services said the lack of electricity did not warrant their investigation.

But months later, authorities were called to the family's home again. This time, they saw more signs of neglect.

One officer found dog feces and urine scattered in the home in December, according to a police report.

During that visit, the officer reported a suspicious bruise on one of the children. But a welfare worker couldn't determine whether it was the result of abuse, the report said. Someone at the house said it may have been caused by a dog.

Police described broken windows and a strong smell of feces in the area where AJ and his younger brother slept.

One officer contacted Crystal Lake Building and Zoning to inspect the home.

"Upon arrival B&Z was denied entry into the residence," the officer wrote.

What happened in AJ's final days

It's still not clear how AJ's life ended, or why.

The boy's father, Andrew Freund Sr., told a 911 dispatcher that he put AJ to bed the night of April 17 but could not find him the next morning.

"I got back from the doctor's appointment and I checked in on him to say good morning and he wasn't there," Freund told 911.

Sonar teams searched Crystal Lake, but found nothing. Canine teams "only picked up Andrew's 'scent' within the residence, indicating that Andrew had not walked away on foot," police said.

A week after AJ disappeared, he was found dead about 10 miles away in the city of Woodstock. The boy's body was wrapped in plastic and hidden in a shallow grave.

The discovery came after investigators analyzed the forensics of the parents' cell phone data. Police then interviewed both parents, who eventually provided information that led to AJ's body, officers said.

Both the father and AJ's mother, JoAnn Cunningham, face charges of first-degree murder, aggravated battery, aggravated domestic battery and failure to report a missing child or child death, Crystal Lake Police Chief Jim Black said.

Freund, the father, also faces a charge of concealment of homicidal death, police said.

It's not immediately clear whether Freund has retained an attorney.

But the mother's attorney, George Kililis, told CNN affiliate WLS before the boy's body was found that Cunningham "is devastated."

The mother "doesn't know what happened to AJ, and had nothing to do with his disappearance," her attorney said last weekend.

Bail was set Thursday at $5 million for each parent.

'We ... are happy you no longer have to suffer'

In the close-knit city of Crystal Lake, devastated neighbors hugged and wept as news of AJ's death spread. Flowers and stuffed animals piled up outside the boy's home.

"Just a little, sweet 5-year-old boy," neighbor Janelle Butler told CNN affiliate WLS. "Oh my gosh, who could do that? I can't believe that I knew them and talked to them and they were capable of doing that. Right across your street."

Butler remembered the last time she saw AJ.

"He was at the door with his brother fighting over who was going to get in the door first," she said.

Black, the city's police chief, spoke openly to AJ and said there's some consolation that mourners can take comfort in:

"We know you are at peace playing in heaven's playground, and are happy you no longer have to suffer."