A Montgomery County babysitter accused of sexually assaulting a 13-month-old girl in his care was charged with murder Tuesday in the baby's Aug. 26 death.

Timothy Conrad Phillips, 30, had been held at the Montgomery County Detention Center on an unrelated theft charge, in addition to charges of second-degree sex offense and child abuse of Amani Renee Robinson.

The state medical examiner last month ruled Amani's death a homicide and determined that she was smothered. In September, the medical examiner determined that the baby had suffered severe sexual abuse. Amani is believed to be one of the youngest sex abuse victims in the county.

Officials have said Phillips, whose last address was in the 700 block of Lenmore Avenue in Rockville, is the leading suspect in the death of Andre Michael Whitworth, a 2-year-old Rockville boy whose mother found him unconscious and badly beaten in his crib after being in the man's care two years ago. The child died at Children's Hospital.

The D.C. medical examiner ruled Andre's Feb. 2, 1997, death a homicide and attributed it to "blunt-force trauma" to the head. No one was ever charged.

Montgomery County State's Attorney Douglas F. Gansler (D) said yesterday that if a grand jury determines that Amani died during a sexual assault, Phillips could be indicted on a first-degree murder charge. Homicides that occur during the course of certain felonies, such as sexual assaults, can be punishable by death, Gansler said.

Gansler said he has not yet determined whether Phillips will be charged in Andre's death.

"We're looking into it, and we'll see what light this sheds on the second case," he said.

According to court documents, about 9:15 a.m. Aug. 26, Phillips, who had offered to care for Amani, called 911, saying a baby had died in a bathtub. When paramedics arrived at Amani's home in the 100 block of Monroe Drive in Rockville, they said they found the baby lying on the living room floor. Neither she nor the bathtub was wet, and her lungs contained no water, officials said.

Phillips, according to police records, rode with paramedics to Shady Grove Adventist Hospital but fled after Amani was pronounced dead.

Police and hospital officials said the child had suffered injuries that appeared to be the result of sexual abuse, according to court documents.

The girl's mother, Amy Hogan, told police she had noticed no injuries while changing her daughter's diaper one hour before Phillips called 911.

Phillips, who surrendered to authorities later that day, was charged Sept. 15 with abusing and sexually assaulting the child. He is being held in lieu of $250,000 bail. Police were waiting for the state medical examiner to determine the cause and manner of death before filing murder charges.

In both cases, Phillips offered to sit with the children on the days they were later found unconscious, according to the children's mothers.

Andre's mother, Deborah, said she returned to her apartment in the 12500 block of Veirs Mill Road on the afternoon of Jan. 31 and found her son badly beaten and unconscious. He was taken by ambulance to Children's Hospital in the District, where he died two days later.

Staff writer Katherine Shaver contributed to this report.