A seven-year-old schoolgirl alerted her bus driver to the fact that she'd found her parents dead at home on Monday morning.
The Pennsylvania girl had got herself ready for school and headed off for the day after she tried to wake her parents but couldn't.
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On the bus ride home she told the driver about her worries. He alerted authorities and police found the bodies of Christopher Dilly, 26, and Jessica Lally, 25, at the home in McKeesport, in Allegheny County, just outside Pittsburgh.
Three other children were also found in the home, aged nine months, three and five. All were unharmed.
According to the BBC, Ms Lally's sister Courtney Lally said she had tried to intervene earlier in the year as she was worried for the children's safety.
She said: "My sister wasn't the person she became when it came to drugs. She wasn't the person I knew. It was like the drugs had taken over and at first we didn't know it was heroin.
"She loved her kids - she did. She loved her mom, she loved me, she loved us."
Courtney said she and her mother plan to attend a hearing on Wednesday to try for temporary custody of the four children.
The Guardian reports that an opioid overdose epidemic is wreaking havoc in Allegheny County. Another man died of an overdose of heroin on the same street earlier that day. A report released in July said that "Allegheny County experienced 422 overdose deaths – more than in any prior year – and the upward trend continues".