A 26-year-old former security guard has been arrested in the violent death of his girlfriend's 4-year-old son, the fourth time this year a child known to Sacramento County's Child Protective Services has died.

The latest case involves young Jahmaurae Allen, who sheriff's officials say was beaten to death inside his mother's Foothill Farms apartment at 4420 Oakhollow Drive early Monday.

Deputies and paramedics arrived at the apartment complex off Roseville Road after receiving a 911 call about an unconscious child at 3:41 a.m. Monday, sheriff's Sgt. Tim Curran said.

The boy, who was home with his 18-month-old sister and his mother's boyfriend, 6-foot-4-inch, 250-pound Jonathan Lamar Perry, was rushed to Mercy San Juan Medical Center with massive head and internal injuries, Curran said.

At 9:30 that night, the boy was transferred to the UC Davis Medical Center, where he was pronounced dead at 11:10 p.m.

This was the fifth suspected child abuse and neglect homicide in the county this year.

CPS Director Laura Coulthard confirmed that four of those children had CPS histories in Sacramento County.

Last month, a five-month Bee investigation revealed that internal problems persist at CPS, despite changes enacted a dozen years ago to protect children. The agency's overhaul followed the 1996 murder of 3-year-old Adrian Conway, whose mother had extensive involvement with CPS before she tortured and beat her only son to death.

Despite an infusion of money and staff at CPS, The Bee found ongoing problems with the agency's training, supervision, investigations and evaluation of children's risk.

In February, a 3-year-old Fair Oaks girl was also beaten to death, and her mother's boyfriend was arrested on suspicion of murder. Valeeya Brazile had been monitored by CPS after her mother was accused of trying to run over a different boyfriend in 2006, but the case was closed six months before Valeeya's death. The coroner found that the little girl was a victim of battered child syndrome and had suffered numerous injuries over time.

Lynn Frank, head of the county's Department of Health and Human Services, which oversees CPS, said through a spokeswoman Wednesday that the case on Jahmaurae was opened June 16. Frank did not elaborate. The county is conducting its own investigation, the statement read, and no one would be available for comment until today.

"While the focus of the investigation is rightly on the person suspected of committing this dreadful crime, we care deeply about what happened to Jahmaurae and wish to acknowledge our role in responding to concerns about his well-being," Frank said in her statement.

Frank wrote a lengthy piece published Sunday in The Bee, praising the hardworking CPS staff and saying that "we err on the side of caution."

"When we determine children have been abused or neglected, we remove them from their homes at a much higher rate than any of California's largest counties," she wrote.

Jahmaurae wasn't removed from his home, despite allegations of abuse a month before his death. The Bee has been unable to review the child's CPS file – which a new state law will make available – but three sources told The Bee that a medical professional had reported suspicious injuries to the agency in June.

Jahmaurae reportedly had a large bruise on his chest, but the social worker thought it could have been caused by his 3-year-old sibling, and the three children were not removed from the home, the sources said.

This week, the boy's mother, 26-year-old Tiffany Lacy, left the apartment early Monday to take the 3-year-old to the hospital for an illness, according to the sources.

Deputies and paramedics arrived after she had left and found Jahmaurae unresponsive inside the apartment with Perry and the 18-month-old.

Detectives continued their questioning of Perry and arrested him at 2 p.m. Tuesday at the home of a relative in Antioch, Curran said. He was being held without bail at the Sacramento County jail pending his arraignment today on charges of murder and child endangerment.

Lacy could not be reached for comment Wednesday. No one answered the door at her ground-floor apartment, where a child's broken plastic basketball hoop, a plastic baseball bat and a Fisher-Price toy lawn mower sat in the tiny yard.

Neighbors said they did not know the residents of the apartment, which is in a complex where each unit is in clusters of four. Some said they had seen sheriff's cars and ambulances at the scene early Monday but knew nothing about the case.

A relative of Lacy's reached at her home in Louisiana said the family had no comment.

Efforts to reach Perry's family were unsuccessful. Calls to an address he has used in the past in Antioch were not returned.

State records show Perry was licensed as a security guard from September 2001 until his license expired two years later, and that he had no record of disciplinary problems.

David Travers, president of Guardian Security Agency in Concord, said Perry had worked for his company for two months and failed to pass his 90-day probation period.

Call The Bee's Marjie Lundstrom, (916) 321-1055. Bee researcher Sheila A. Kern contributed to this report.