CHICAGO (STMW) — An autopsy Saturday determined a four-year-old boy died Friday from child abuse and his death was ruled a homicide.

It was Christopher Valdez’s fourth birthday Friday, and his relatives were preparing to celebrate at the family’s Southwest Side home. But instead of a celebration, there was mourning.

The little boy was killed Friday afternoon in what police described as a “possible domestic situation,” at Christopher’s home in the 5100 block of South Trumbull Avenue.

Police late Friday said they were talking to a male person of interest who was in custody in the case. No charges have been filed as of Saturday night.

Police said the boy was dead when police arrived at the home about 2:10 p.m. Friday. The child appeared to have died from “multiple blunt force trauma,” police said.

The boy was pronounced dead at Holy Cross Hospital at 3:10 p.m., according to the Cook County Medical Examiner’s office.

An autopsy Saturday determined that Valdez died from multiple blunt force injuries and child abuse, according to the medical examiner’s office. His death was ruled a homicide.

On Friday night, shocked relatives gathered at the home of Christopher’s grandparents — just across the alley from where Christopher lived — to grieve. And they defended the boy’s mother.

“We want everyone to know that our daughter is innocent of whatever happened there,” said Christopher’s grandfather, Tom Valdez.

While the family said they didn’t yet know all of the details, they said that at some point Friday afternoon, Christopher’s mother, Crystal Valdez, telephoned one of her brothers, desperate for help.

Upon arriving at his sister’s home, the brother was forced to restrain his sister’s live-in boyfriend, with whom Crystal Valdez had a troubled relationship, family members said.

“He has created a lot of problems,” said Tom Valdez, declining to go into details.

(Source: Sun-Times Media Wire © Chicago Sun-Times 2010. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)