A Texas nurse once dubbed an “Angel of Death” killer has been indicted in the 1981 slaying of an 11-month-old boy who she injected with a toxic dose of anti-seizure medication, authorities said.

Genene Jones, 66, was indicted by a grand jury Thursday, more than three decades after Joshua Sawyer’s death. Authorities suspect that Jones, who is already serving a 99-year prison sentence in the death of another child, might have killed up to 60 young children during her time as a nurse in the pediatric intensive care unit in the former Bexar County Medical Center Hospital in San Antonio, according to the Bexar County district attorney’s office.

Authorities have long suspected that Jones was connected to a series of infant deaths in the 1980s at hospitals in San Antonio and nearby Kerrville, according to the San Antonio Express-News.

Prosecutors said evidence shows that in December 1981, Jones gave Joshua a lethal dose of Dilantin, or phenytoin, which is used as an anti-seizure medication. The Washington Post reported in 1983 that investigators were pulling hospital records to determine what had caused the dozens of unexplained deaths, and grand juries in two Texas cities were hearing testimony in the case. The next year, prosecutors said, Jones was convicted of murder and sentenced to 99 years in prison for the death of 15-month-old Chelsea McClellan, who was injected with a potent muscle relaxer and died in 1982.

Jones is scheduled for release in Gatesville in March 2018, according to records from the Texas Department of Criminal Justice, pursuant to mandatory release regulations at the time of her conviction. Before that, prosecutors said, Jones will be extradited to Bexar County, where she will stand trial in the new case.