Montgomery County officials have reopened the investigation into the death of an infant in the care of a Germantown couple later convicted in one of the region's most gruesome child abuse cases for their treatment of the dead child's half brother.

The March 1997 death of 6-month-old Alexander Holmes had been attributed to sudden infant death syndrome, but the state's top medical examiner has changed the ruling to "undetermined causes." John P. Smialek, the state's chief medical examiner, refused yesterday to say what prompted him to review the case.

The child abuse occurring in the home of Alba Ingrid Scarpelli and Alan Lee Holmes came to the attention of county authorities when the couple called paramedics because Alexander was unresponsive.

While the couple went to the hospital with the infant, they left Holmes's 5-year-old son and Scarpelli's 3-year-daughter with neighbors who reported that the two children were malnourished and appeared abused, authorities said.

When Alexander died, his death was ruled a SIDS case, closing that investigation.

But the investigation into the abuse of the older boy continued, and Holmes and Antonelli were convicted in 1997 of torturing him in what county authorities called one of the worst such cases in years. Scarpelli was convicted of force-feeding the boy hot peppers and whiskey, tethering him to a bed with a cat leash for up to 22 hours a day, taping his mouth shut and binding his wrists and ankles. Holmes was convicted of standing by as that happened.

The abuse occurred after the 5-year-old had been returned to his father's home despite the father's 1992 conviction for neglecting the same child.

Smialek said he did not know whether Montgomery County police told the medical examiner performing the infant's autopsy the history of child abuse in the family. "I'm not sure how much of that information was available," Smialek said. He said he also was unsure whether the medical examiner who performed the autopsy and ruled that the cause of death was SIDS requested such information.

The changed ruling on the infant's death "didn't come as much of a surprise to me," Montgomery State's Attorney Douglas F. Gansler said. "Given the circumstances as we know them, it's very hard to imagine that's a SIDS death, but we haven't gone to the next step to determine what it was."

Gansler declined to comment on whether Scarpelli or Holmes had been interviewed again about Alexander's death. Gansler said his office began to "reassess" Alexander's death two weeks ago, after the medical examiner's office passed along the word about its new ruling.

Gansler was not the prosecutor at the time of the baby's death or his half brother's abuse case. A spokeswoman for Montgomery Police Chief Charles A. Moose, who also is new in his job, said he declined to comment.

The original autopsy on Alexander found a small area of blood just beneath the covering of the child's brain, perhaps the result of a blow or a fall that triggered a slow, week-long hemorrhage, Smialek said. Neither the child's brain nor his skull was injured, according to the March 1997 autopsy, which found "no evidence of significant recent injury, abuse or neglect."

The new "pathological diagnosis" notes that the apartment where the baby lived was "filthy" and mentions the severe abuse and neglect of his half brother.

During the original investigation, "the medical examiner was operating in a vacuum," Gansler said. In reclassifying the death, Smialek "had more of the picture."

Scarpelli's attorney, Harry J. Trainor, said there is scant evidence supporting Smialek's decision to change the ruling. He said the "state's successful prosecution" of Garrett Eldred Wilson may have been a motivation.

Wilson received a life sentence this month for murdering his infant son to collect life insurance. The child's manner of death originally was classified as due to SIDS but was changed to homicide.

Robert M. McCarthy, the attorney for the 5-year-old son in the child abuse case, said Smialek has "taken the ruling from SIDS to undetermined, which tells us nothing." Reporters from the television show "Dateline" also had begun asking about Alexander's death, McCarthy said, adding that that might have driven the change in the ruling. Gansler acknowledged the reporters' inquiries.

Holmes remains jailed for abusing his 5-year-old son. He was sentenced to 10 years after a judge said he was more responsible because he stood by and let Scarpelli abuse his own son. Scarpelli was sentenced in February 1998 to six years, with all but 18 months suspended. With credit for good behavior, she was released after 14 months and has since given birth to another daughter.

Holmes's older son, county officials said, is in a foster home. Scarpelli's older daughter lives with her grandfather, and the infant girl lives with another relative, officials said.