Brenda Aguero, 27, was arrested Friday by order of prosecutor Raul Garzon, who is investigating the deaths of five newborns at the Neonatal Maternity Hospital in Cordoba, 435 miles (700 kilometers) northwest of Buenos Aires.

Garzon told local media that the nurse has been charged with the murder of two babies pending review of the medical records of three other infants.

“The babies died because a substance found in their bodies was incompatible with life,” Garzon said, adding that an excess of potassium was discovered.

In addition, he said, eight other newborns were sickened but did not die.

He said the deceased babies were born healthy, and their mothers’ health was good at the time of delivery.

The deaths occurred between March and June, but the case came to light only after the grandmother of a baby who died June 6 filed a complaint.

Garzon said there were “reasons to presume” the suspect’s responsibility.

The nurse is one of nine people suspended this month after an investigation was opened to determine whether the deaths were due to homicide, negligence or malpractice.

Three former hospital officials have been charged with failure to carry out official duties.

“We are devastated as a family,” Raul Aragon, the father of one of the dead infants, told a Cordoba radio station.

“We were trying to overcome and mourn a natural death, and now we learn that they took our son from us – that they killed him.”