Diane Staudte, 51, of Springfield, was charged Friday with two counts of first-degree murder, one count of first-degree assault and one count of armed criminal action. Her daughter, Rachel Staudte, 22, was charged with the same counts Saturday.
Both women are jailed without bond. A spokeswoman for the Greene County prosecutor's office didn't immediately return an email Saturday from The Associated Press. It wasn't clear if the women had attorneys.
Diane Staudte initially told law enforcement that her husband, Mark Staudte, 61, hadn't been feeling well and suffered from seizures before his April 2012 death, the probable cause statement said. And she said her son, Shawn Staudte, 26, had been sick with flu-like symptoms before his death in September.
The medical examiner in Greene County at first ruled that the husband died of natural causes and the son as a result of prior medical issues. But an anonymous tip led authorities to re-examine the deaths earlier this month following the hospitalization of Diane Staudte's daughter, 24-year-old Sarah Staudte, the statement said.
A detective wrote that a nurse told him that although Sarah Staudte's condition was potentially fatal, Diane Staudte had visited only a couple times and not stayed long.
A doctor told the detective that Sarah Staudte's condition was "very suspicious" and said he suspected the young woman had been poisoned.
Diane Staudte admitted under questioning to poisoning her family by putting antifreeze in their soda and Gatorade over several days, the statement said.
She told the detective that she killed her husband because she "hated him" and her son because he was "worse than a pest." She said she wanted to kill her daughter, Sarah, because the young woman "would not get a job and had student loans that had to be paid," the probable cause statement said.
The Springfield News-Leader, citing the probable cause statement in Rachel Staudte's case, said Diane Staudte originally told police she was the only one involved. But the statement said that when Rachel Staudte was confronted with evidence, she admitted to taking part in the deaths and assault.
During a subsequent interview, Diane Staudte then admitted that she and Rachel Staudte had planned, researched and committed the crimes together, the statement said.