Not knowing what the hidden camera had captured, McCallister's daughter and son-in-law, Mary and Paul Franch, showed up for one of their regular visits with the woman five minutes after the abuse had taken place.
They described McCallister as agitated, and she repeatedly asked them, "Why do they keep picking on me?" according to the affidavit.
The couple went to nursing home officials in early March, saying that McCallister told them she'd been hit and slapped.
Quadrangle officials attributed the allegations to the woman's dementia.
After spotting bruises on the woman's wrist and left hand, McCallister's daughter and son-in-law had the camera installed.
"Many dementia patients can communicate some things in a way that is somewhat lucid if you know them well and work with them on a regular basis as these folks [the French couple] did," District Attorney Green said.
McCallister is now living with her daughter and son-in-law.
The organization that runs the Quadrangle facility, Sunrise Senior Living, issued a statement saying that the employees in the video have been fired.
"Our number one concern, above all else, is the safety of our residents. We have a number of policies and procedures in place that address their welfare and are intended to prevent any inappropriate activity in our community," said executives in a written statement.
Brent Russell from Sunrise Senior Living told ABC affiliate WPVI that they were cooperating with police in the investigation.
"Any harm that comes to any of our residents, we are certainly the people who are most eager to make sure that justice is done," Russell said.
The video that was taken is legal because it had no audio, and McCallister's daughter and son-in-law had legal authority over the elderly woman to put a camera in her room, Green said.
The Pennsylvania Department of Public Welfare has also launched a separate investigation into the alleged abuse.