Their mother, 49-year-old Janette MacAusland, is charged with two counts of first-degree murder. The charges are allegations, and she has not been convicted.

The medical examiner found four drugs in the children’s systems, including zolpidem and lorazepam, medications commonly prescribed for insomnia. The findings were released this week, after prosecutors told a court last month they needed more time to develop the case while awaiting the cause-of-death determinations.

Dr. Knarik Arkun, director of neuropathology and autopsy at Tufts, said the presence of both causes may indicate that the children had significant drug levels. “If someone is sleepy, they cannot struggle, they cannot fight back,” she said.

Police have said MacAusland told an officer she strangled the children and then tried to kill herself. She was arrested in Vermont after the children were found. A Norfolk County grand jury later indicted her, moving the case to Superior Court.

The drug findings could figure in the prosecution’s effort to prove premeditation, said Michael Coyne, NBC10’s chief legal analyst. He said prosecutors may argue that giving the children medication before their deaths showed planning. MacAusland’s attorney has said mental illness could play a role in her defense.

MacAusland is scheduled to be arraigned in Norfolk Superior Court at 2 p.m. Nov. 3. Her attorney did not respond to a request for comment Thursday.