Child advocates are asking what went wrong after seven-year-old Katelynn Sampson was abused and eventually murdered by her caregivers in a Parkdale apartment in August 2008.

On Tuesday, the girl's former caregivers, Donna Irving and Warren Johnson, pleaded guilty to Katelynn's second-degree murder and were sentenced to life in prison with no chance of parole for 15 years.

The little girl's death came months after Katelynn's school principal noticed bruises on the little girl's body and reported suspected abuse to the Children's Aid Society.

The case was passed between the Children's Aid Society and Native Child and Family Services, with neither agency acting in the days leading up to Katelynn's death on August 3, 2008.

The Children's Aid Society said it faxed Katelynn's case to Native Child and Family Services, but failed to follow up to make sure the other agency got the fax.

Native Child and Family Services executive director Kenn Richard said his agency didn't get the case.

"We've investigated this as far as we can go," Richard said. "No indication that we received a referral from anybody on Katelynn at that time."

In his ruling Tuesday, Justice John McMahon said that the system failed Katelynn, who was removed from her school without anyone investigating and was abused daily for 72 days before her eventual death from septic shock, caused by untreated wounds all over her body.

"The alarm bells were ringing, but no one was responding," McMahon said Tuesday during his ruling.

Still, the agencies responsible for her file say there is no way they could have known about Katelynn's situation from the information they had.

"There's a long way from the information that we had, to an event like the homicide of a small child like Katelynn Sampson," said Richard.

There have also been process changes since Katelynn's death, said Children's Aid Society of Toronto executive director David Rivard.

"Between the four Children's Aid societies, there's been a tightening of how information is exchanged," Rivard said.

Besides the mismanaged case file, court heard that Family Court also failed the little girl by not checking Johnson's background or criminal record in June 2008, before granting her custody of Katelynn.

At the time, Katelynn's biological mother, Bernice Sampson, was dealing with her own addiction to crack-cocaine. Johnson had been a friend to Katelynn's mother for a decade.

Court heard that Johnson lied to Family Court and that she previously had two of her own children removed by Children's Aid before she gained custody of Katelynn.

Assurances of process changes to how children's agencies handle case files isn't enough for the province's child and youth advocate, who is calling for a coroner's inquest into Katelynn's death.

"We have to look at Katelynn's life and fearlessly examine it and see where we, as a province, can do better," said Irwin Elman.

Native Child and Family Services said it would support an inquest.

Still, provincial ombusman Andre Marin said even an inquest would not go far enough, suggesting that the Child's Aid Society needs a better oversight body.

"There's a good reason why these cases fall through the cracks -- it's that there is no outside agency that investigates the administrative decisions of the CAS," said Marin.

With files from CTV Toronto's Tamara Cherry