Relatives of a man who took part in the brutal beating of a young Manitoba girl are asking for anonymity when they testify at an inquiry into her death.

Three of Karl Wesley McKay's children and a former common-law spouse have applied for a publication ban on their names.

They say they fear harassment or physical harm if their ties to McKay — something they have kept hidden for years — become public knowledge.

"I am currently going to school. No one connected to my schooling is aware that I am related to Wes McKay," reads an affidavit from one of McKay's kids.

"I have serious concerns that if my fellow students and teachers were to become aware of my relationship to Wes McKay, that I would suffer serious consequences ranging from verbal harassment to possible physical harassment."

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Karl Wesley McKay, right, is seen in this police interrogation video following his arrest. He and Samantha Kematch were convicted in 2008 of first-degree murder in Phoenix's death. (CBC)

Another child says in a separate affidavit that McKay's murder conviction has been kept a secret from McKay's grandchildren.

"My children do not know that their grandfather was convicted of the murder of Phoenix Sinclair. Although I may advise them of this information at some time, I do not wish to have this information made known to them now."

Commissioner Ted Hughes is expected to set a date Thursday for a hearing on the publication ban request.

In the meantime, he has ordered that the names and photos of the four relatives must not be published, although their relationship to McKay can be described.

The inquiry, which began last fall, is examining how Manitoba child welfare failed to protect Phoenix. The girl was taken into foster care shortly after her birth in April 2000, then bounced between foster homes, family friends and her divorced parents.

In 2004, she ended up in the custody of her mother, Samantha Kematch, and McKay, the woman's new boyfriend.

Social workers failed to realize that he was the same Karl McKay who had a long history of domestic violence outlined in the province's child-welfare database.

In June 2005, McKay and Kematch beat Phoenix to death on the concrete basement floor of their home. They were convicted of first-degree murder and are serving life sentences.

Their trial was told Phoenix had suffered horrific abuse that included being shot with a BB gun and being forced to eat her own vomit.

Social workers opened and closed Phoenix's file several times throughout her short life. In March 2005 they received an anonymous tip that Kematch was abusing her daughter.

They went to talk to Kematch, but left without seeing Phoenix and closed the file a final time.