Miss Powell, who has two teenage children, was arrested at her home in Llangennech, near Llanelli last week following claims that she was in possession of a letter written by Brady that could identify the location of Keith Bennett, the only victim whose body has never been found.
Anger over suggestions that Miss Powell had withheld information intensified over the weekend following the death of Keith's mother Winnie Johnson.
The 78-year-old, whose 12-year-old son was murdered by Brady and his accomplice Myra Hindley in 1964, fought tirelessly to discover the location of her son's body so she could give him a proper burial.
Police acted on Thursday after being informed by a Channel 4 documentary maker that Miss Powell had been given a letter to be opened in the event of Brady's death.
She allegedly told the filmmaker the letter could contain details of Keith's whereabouts as there were secrets Brady did not want to take with him to the grave.
Yesterday Keith's brother Alan, urged the police to continue searching for his brother's remains in tribute to his mother's memory.
Writing on his website, he said: "As far as I am concerned, until Keith is found then he is still in the possession of Brady and Hindley.
"Our fear as a family is that now my mother is no longer with us, this may be seen by the police and the media as some sort of closure to the case.
"This must not be allowed to happen both out of respect for Keith and my mother's memory and for those of us who loved them both."
Mrs Johnson's dying wish was reportedly that Keith's body be laid to rest alongside her if his remains are ever found, it was reported last night.
A source close to Mrs Johnson told a newspaper: "There is a family grave where she wants to be buried. If Keith was found, which was always the hope, then he would be brought back for a proper burial."
Miss Powell, who has acted for Brady since 1999, left her home on Friday amid warnings that she could be targeted by those angry at her close association with him.
Donna Armstrong, 28, who lives close to Miss Powell and her family said: "There have been neighbours outside the house chanting and saying for her to get out and stay away.
"Since then police have been circling around a lot. It is very worrying for such a quiet place."
Fellow neighbour Wendy Williams, 35, said locals in the quiet community were concerned that Miss Powell's links to Brady could lead to vigilante attacks.
She said: "It's worrying for us because we don't know if someone might take up against her."
Fellow neighbour Tracey Jones added: "I don't know how anyone can represent Brady knowing the evil things that he did. You don't expect someone like that to be living in a little Welsh village. Frankly we don't want her living here and I hope she doesn't come back."