The death penalty is being sought by prosecutors against a couple who have been charged with the torture and murder of the woman’s three-year-old son in what was described as “an American horror story”.

Jillian Tait and her boyfriend, Gary Lee Fellenbaum, were said to have had sex, went shopping and ate pizza as toddler Scott McMillan lay dying on 4 November after alleged incidents of escalating violence by the pair including, it is claimed, beating him with a frying pan and hanging him upside down by his feet.

Fellenbaum is alleged to have used electrical tape to trap the boy in his seat while he abused him and investigators said that he had left him in the shower for 30 minutes while he was unresponsive. The alleged crimes could be punishable by death in the US as prosecutors claim the boy died by torture and he was under 12 years of age.

The last prisoner to have been executed by the state of Pennsylvania was Gary Heidnik in 1999 by lethal injection for kidnapping, torturing and raping six women and keeping them detained in his basement in Philadelphia.

District Attorney Tom Hogan said he is seeking the death penalty against the couple saying the abuse had been so horrific that medics were reported to have cried at the sight of the boy's bruised and punctured body after he was rushed to hospital following at least weeks of alleged violence that, it is claimed, had intensified during his last three days, as reported by 6abc Philadelphia.

Scott McMillan died after many weeks of violence (AP)

Huge dents in the wall were found by investigators next to the mattress that Scott was seemingly put on after he was allegedly beaten and Tait claimed in a police statement that they were caused by Fellenbaum hitting the boy’s head against it in response to him refusing to eat his toast before he died.

Tait, 31, and Fellenbaum, 23, pleaded not guilty to the indictments, which include murder and child abuse, on Wednesday after they were formally charged. Their hearing was made by video link to where they are detained in Chester County prison, Pennsylvania.

Fellenbaum’s ex-wife Amber, 21, has also been charged with child endangerment for allegedly witnessing the beatings and not doing anything about it until she finally called emergency services when the boy was unresponsive. She had lived in the same mobile home as the couple along with two other children, a boy aged six and an 11-month-old girl, in Coatsville, Pennsylvania. It is alleged that the six-year-old boy was also beaten.

Chester County District Attorney Thomas Hogan called the case “an American horror story” and that “it was an unspeakable act of depravity”. He added that it “was just evilness” as there was no evidence that the pair had been drinking or using drugs.

The US has one of the worst child abuse records in industrialised countries with between four and seven children dying from violence and neglect every day, according to the Childhelp charity.