"You're all waiting for that last thing to come forward that says, 'This is what caused the death of child number one and child number two.' Unfortunately we didn't get that until today," Bellefontaine police chief Brandon Standley told reporters.
A 23-year-old Ohio woman has confessed to killing three of her four children.
Brittany Pilkington of Bellefontaine, Ohio is accused of the killings. She told police she did it because the boys were getting more attention than their sister from the father.
Three-month-old Noah died Tuesday. His mother called 911 when he stopped breathing.
"911, what's your emergency?"
"Our son is on an asthma monitoring system. It's going off. He's not breathing," Pilkington said in the 911 call.
This came after the deaths of her 4-year-old son Gavin Pilkington in April and 3-month-old son Niall Pilkington in July 2014.
The Columbus Dispatch reports Noah and his sister Hailey were taken into protective custody. Noah was returned earlier this week after a coroner couldn't find anything suspicious about the other two boys' deaths.
But when Pilkington was talking to police Tuesday, she admitted to smothering the boys with a blanket.
Her father spoke with WCMH: "I can't even believe it. ... I hope she don't get off, I mean, scott-free."
Pilkington is now facing three counts of murder.