According to the police recording, Snyder called the emergency services on September 23 and told the operator she had found her children hanged from a beam in the basement.
She claimed Connor had been bullied by kids at school and had threatened to commit suicide in the past.
But in court, prosecutors have rubbished those claims, arguing Connor was a happy child shortly before his death.
After Synder's 911 call, two children were rushed to hospital and transferred onto life support machines.
But despite medics' best efforts, they died three days later.
In December, Synder was charged with the first-degree murder of Connor and Brindley.
She was also charged with third-degree murder, tampering with evidence, endangering the welfare of children, animal cruelty and sexual intercourse with a dog.
Prosecutors argued there were five aggravating factors that warranted the death penalty, including the ages of the victims, according to the Morning Call.
Synder will return to court for a case status hearing on June 29.