That blow might have killed Faheem Williams, whose mummified remains were found stuffed into a plastic storage bin, two law enforcement sources who spoke on condition of anonymity said Saturday.
"It appears that way," said one of the sources.
An autopsy determined Faheem died from starvation and blunt force trauma to the stomach, and his death was ruled a homicide. No one had been charged with killing the boy by Saturday.
Wesley Murphy, 16, was arrested Friday night and charged with aggravated assault and two counts of child endangerment.
His mother, Sherry Murphy, had been responsible for caring for Faheem; his twin brother, Raheem; and their 4-year-old brother, Tyrone Hill, since the boys' mother, Melinda Williams, went to jail in March 2002.
Wesley Murphy said his blow knocked Faheem unconscious, and Sherry Murphy tried unsuccessfully to revive him, the sources said. After the boy died, the teen and his mother conspired to hide the body and the two surviving children, they said.
The wrestling match took place in September in an Irvington home where Murphy and the children lived before moving to Newark about two months ago, the sources said. That would mean Faheem's dead body was moved to the Newark apartment where it was discovered on Jan. 5.
Sherry Murphy has pleaded innocent to endangerment charges. An arraignment for Wesley Murphy was not immediately scheduled. A call seeking comment from the Essex County Public Defender's Office was not immediately returned Saturday.
In an interview with The Star-Ledger of Newark before he was arrested Friday, Wesley Murphy said he was eager to talk with police because he thought his mother was being unfairly accused of child abuse.
"If I knew more stuff to help my mother, I would," he told the newspaper.
He told the newspaper he suspected Faheem's mother had killed him to prevent him from speaking of abuse he had suffered.
Melinda Williams, who had been jailed for a child endangerment conviction, was freed in August and has said she could not find Murphy or her children. It could not be immediately determined whether the charge involved one of her three boys.
The case came to light when Murphy's boyfriend went looking for his boots in the basement on Jan. 4. He broke down a locked door, and found Raheem and Tyrone cowering under a filthy bed.
Newark Police Lt. Derek Glenn said the boyfriend, who has not been charged, apparently was unaware the children were hidden in the basement.
At a hospital, Raheem told investigators he had a twin brother he hadn't seen for a while. The next day, police and a cadaver-sniffing dog found Faheem's body in a plastic storage bin in a closet.
The state Division of Youth and Family Services had investigated complaints of abuse involving Williams' children since 1992, but never sought to remove the boys from the home.
The case prompted Gov. James E. McGreevey to order a sweeping review of the agency's handling of other cases. The review has found systemwide shortcomings, particularly in the sharing and use of information, officials said.
"There are serious problems in this case. The problems speak both to human error and policy issues," said N.J. Human Services Commissioner Gwendolyn Harris.
The state's child services agency has asked police to help find 110 children in suspected abuse cases who social workers were unable to locate during a canvass ordered after the 7-year-old's death.
Since the review was ordered Wednesday, social workers have found 170 children under the agency's supervision. But the Division of Youth and Family Services said it was calling on local police departments to help find the others, and, in some cases, halting welfare payments until parents produced the children.
Human Services Commissioner Gwendolyn Harris declined to say if workers found any new instances of abuse or other problems involving the children who were located.