The mother of missing toddler William Tyrrell has denied any role in his disappearance, urging her son's kidnapper to "let him come home" more than three years after he vanished.
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Karlie Tyrrell also said the foster parents looking after her son when he went missing at the age of three had "failed" him and should feel guilty.
William Tyrrell vanished as he played in his foster grandmother's front yard on the NSW Mid North Coast the morning of September 12, 2014.
His disappearance sparked a mammoth police investigation and generated widespread public concern.
However, legal restrictions prevented his foster status and the identity of his biological parents being revealed until last year.
Speaking publicly for the first time, Ms Tyrrell told Channel Seven's Sunday Night she isolated herself as she "felt like the worst mum in the world".
"Because I haven't come out and said anything, of course, people are gonna assume I don't care.
"And that's OK, because I know that I do.
"Their judgement doesn't bother me, really. I'm not a bad person. I'm not a bad mum."
Ms Tyrrell said she made "bad choices" when her eldest daughter was born and fled with William after the girl was taken into foster care.
"Because I had domestic violence and drugs and alcohol, marijuana. When I had to do a drug screen, I tested positive after I'd had my children."
Despite her efforts to keep William, he was taken to live with the same family when he was nine months old.
It was during a trip to the coast a few years later, as his foster mother and grandmother sipped tea metres from where the two siblings played, that William disappeared.
"They were responsible for looking after him, and they failed," Ms Tyrrell said.
"She went inside and made a cup of tea. If that's the case, like, OK, that's an accident, and that's unfortunate, but it doesn't make any sense to me. Kids don't just go missing."
William's foster mother, who still cares for his older sister, also told Channel Seven of her heartbreak:
"We need to know where he is, and we need to know what happened to him, 'cause we can't live forever like this."
Ms Tyrrell said she didn't speak out around the time William went missing because she "thought it was best".
"They know what they're doing. Like, I didn't wanna go on news being, like, angry or anything, making anything worse."
She was shocked when police knocked on her door to search for William in the initial stages of the police probe.
Ms Tyrrell maintained she had nothing to do with her son's disappearance and had been shopping at Blacktown, in Sydney's western suburbs, at the time.
"I showed the police my ATM receipt, my docket, everything."
Forensic psychologist and former cop Brad Jones said it was "very likely" the veil that surrounded William's biological parents made the investigation more difficult in its early stages.
Ms Tyrrell said she shared the hopes of investigators and some experts that William was still alive, pleading with her son's kidnapper to not hurt him.
"Where else could he be? He's not in the bush ... I feel like whoever has him needs a bullet.
"Just let him come home. Please. It's not fair. This isn't fair."
The NSW government last year offered an unprecedented $1 million reward for any information leading to the toddler's recovery.
Crime Stoppers - 1800 333 000
