COATESVILLE, Pa (AP) — A Pennsylvania couple went car shopping, bought pizza and engaged in sexual activity as the woman’s unresponsive 3-year-old son lay dying after weeks of escalating abuse that ended in three days of systematic torture, authorities said Thursday.Jillian Tait, 31, and Gary Lee Fellenbaum, 23, were charged Thursday with murder in the death of Tait’s son, Scott McMillan, and aggravated assault in the beating of his older brother.They are accused of laughing as Scott was hung upside down and whipped, striking him repeatedly with a frying pan, and eventually beating him to death.Chester County District Attorney Thomas Hogan called the case “an American horror story.”“It was an unspeakable act of depravity,” he said.The couple met working at Wal-Mart and last month moved in together, along with Fellenbaum’s estranged wife and three children — Tait’s 6- and 3-year-old sons and the Fellenbaums’ 11-month-old daughter. The six lived in a mobile home park outside the city of Coatesville, about 35 miles northwest of Philadelphia.The prosecutor said what started as spankings morphed into “concentrated, repeated, escalating abuse.” Then, “over three days he was systematically tortured and beaten to death,” Hogan said.The three adults told authorities “that Scott McMillan had been punched and beaten with blunt and sharp objects, whipped, taped to a chair with electrical tape and beaten, hung up by his feet and beaten, and suffered other acts of violence,” police said in affidavits released Thursday.“During one incident,” the affidavits say, “Gary hung Scott and (his older brother) up by their feet one at a time and beat the boys while they were hanging upside down.