Teen-Ager Held in Death of Baby : Van Nuys: He admits causing the head injuries that killed his girlfriend’s child but says they were inflicted during rough play.

A 16-year-old Van Nuys boy has been arrested on suspicion of murdering his girlfriend’s 23-month-old son, who died Sunday of complications from head injuries, Los Angeles police said Monday.

The teen-ager, whose name was not released because he is a juvenile, was being held at Juvenile Hall in Sylmar, said Lt. Al Moen.

The boy has admitted causing the injuries suffered by Jesus Aguilar, saying they were accidentally inflicted during rough play, Moen said.

But doctors who examined the toddler said the injuries--a fractured skull, broken clavicle and bruises to the face and buttocks--did not occur in the manner described by the youth, Moen said.

The case came to light Saturday about 5:15 p.m. when Jesus was brought by ambulance to Valley Presbyterian Hospital in Van Nuys. He died there about 14 hours later.

Doctors treating the toddler notified police that they suspected child abuse, Moen said. Police then interviewed the toddler’s mother, 18-year-old Josie Aguilar, her teen-age boyfriend, and several other people who live with the couple in a house in the 8000 block of Woodman Avenue, Moen said.

The investigation led to the boyfriend, who is not the baby’s father, Moen said. “He was the last person to have the care and custody of the child,” Moen said.

Police believe the abuse occurred Saturday morning, when the teen-ager was left alone with the child.

When Josie Aguilar, who is pregnant with her boyfriend’s child, returned home, she discovered that Jesus was unconscious, Moen said. An ambulance was called and the child was taken to the hospital.

The teen-ager has said the injuries were not deliberate, Moen said.

“Basically, he described that he was rough-playing with the child, basically tossing the child,” Moen said. But Moen said the boy was not immediately taken to the hospital and that police “don’t put a lot of credence” in the boy’s story.

The police plan to discuss with the district attorney’s office whether to try the teen-ager as an adult. Authorities said they know of no motive for the crime.