By Brad Segall

WEST CALN TOWNSHIP, Pa. (CBS) — Authorities in Chester County, Pa. say they will pursue the death penalty against a mother and her boyfriend who remain behind bars, accused of torturing and beating her three-year-old son to death in early November.

Gary Fellenbaum and Jillian Tate appeared in court today for their formal arraignment, where they pleaded not guilty to first-degree murder and related offenses.

Over the course of three days, prosecutors say, the defendants systematically tortured Scotty McMillan in their West Caln home until he died of multiple blunt force trauma.

Chester County DA Tom Hogan says there are two aggravating factors that make this a death-penalty case:

“The first is that a child under the age of 12 was killed — in this case Scotty McMillan was three years old.  The second is that this child was killed by torture.”

Fellenbaum’s wife, Amber, who also lived in the house, faces child endangerment charges.

Gary Fellenbaum and Tait remain behind bars without bail.  When the two were arrested, Hogan described the death as “an American horror story.”