BOSTON -- A Plymouth County grand jury has decided not to charge a Tufts Medical Center psychiatrist in connection with the death of a 4-year-old Hull girl who died after an overdose of drugs in 2006.

The grand jury investigated the actions of Dr. Kayoko Kifuji who treated Rebecca Riley for bi-polar disorder and prescribed several drugs, some of which were found in the child's system when she died.

Riley's parents, Michael Riley, 36, and Carolyn Riley, 34, are awaiting trial on second degree murder charges, both accused of killing her with an overdose on Dec. 13, 2006.

A police investigation showed the child had been prescribed clonidine for attention deficit hyperactivity disorder and valproic acid and Seroquel for bipolar disorder. The medical examiner's autopsy indicated that she died from a toxic combination of clonidine, Depakote, dextromethorphan, and chlorpheniramine.

The district attorney's office called the death an intentional overdose.

The Riley's other two children, ages 11 and 6, were placed in foster care after Rebecca's death.

An attorney representing the girl's estate has since sued Kifuji for malpractice.