Damon Decree Sr. spoke to ABC11 on Tuesday and he said that although he was surprised they would hurt their own family, he wasn't surprised something strange was going on.
His estranged wife, 45-year-old Shana Decree and their daughter, 19-year-old Dominique Decree, were both charged with five counts of murder.
The five family members killed have been identified as: Shana Decree's children -- Naa'Irah Smith, 25, and Damon Decree Jr., 13 -- Shana's sister, Jamilla Campbell, 42, and Campbell's 9-year-old twin daughters, Imani and Erika Allen.
"This been going on for the past month," Decree Sr. told ABC11. "I mean we been calling children's services, calling the police."
"From my niece, apparently they had dissected into some type of cult that they materialized online," he said. "I don't know how, what kind of cult. And they were talking about demons being all around them."
He said that if his wife and daughter committed the crimes, he wants them held accountable.
"I don't want them in no insane asylum," he said. "I want to see them in jail for the rest of their life."
ABC11's sister station WPVI was told Children and Youth Social Services Agency did, in fact, perform a welfare check at the apartment where the family lived on Saturday, but when no one answered, a worker left a card.
According to an affidavit of probable cause, representatives returned to the apartment for an unannounced visit around 4 p.m. Monday. When nobody answered, the representative had a maintenance worker open the apartment.
Shana and Dominique Decree were found in bed. The worker reported that the two seemed disoriented and the apartment was in disarray. Local police were called to the scene and both women were taken to the hospital.
Arriving officers saw furniture upended in the apartment, along with broken glass and clutter. The Children and Youth representative told police the apartment was not in disarray during their last visit in early February.
"We've been calling and checking and doing everything we needed to do," Decree Sr. said. "Every time they went from my perspective at least, they said the kids were safe and it's nothing we could do."
Police initially saw four bodies in a small bedroom. The fifth was later discovered underneath another body.
Authorities say Dominique had visible injuries to her neck and, at first, denied knowing what happened. She claimed that an unknown man hurt her and she kept repeating she wanted to die.
Shana also first denied knowing what happened, according to police, claiming her sister's boyfriend and two strange men came into the apartment and killed everyone except her and her daughter.
Dominique separately then echoed claims about her aunt's boyfriend and two unknown males.
The affidavit indicates that later, Shana told police everyone in the apartment, including the 9-year-old twins and 13-year-old, wanted to die and were talking about suicide.
According to the affidavit, Dominique then told police how each person was killed. Dominique said Shana killed one twin, the 13-year-old, and Smith; that Campbell killed the other twin; and she then strangled Campbell.
Police say Shana also gave them an account of who did the killings. Her account varied slightly from her daughter's, saying Dominique helped her with one of the killings and that Campbell killed Smith.
WPVI contributed to this report.