WASHINGTON — An ex-convict likely had help from others holding a family captive inside their mansion for at least 18 hours, authorities said.

During their ordeal, the business executive and his wife told others to stay away — even ordering a pizza deliverer to leave two pies at the door — as they frantically arranged for $40,000 in cash to be dropped off at the home.

But once the money was left on the seat of a red sports car in the family’s garage, Daron Dylon Wint struck and stabbed Savvas Savopoulos, the CEO of the American Iron Works company where he had once worked as a welder, Wint’s charging document said. At a court hearing Friday, Wint was ordered held in jail on a murder charge.

Savopoulos’ wife, Amy, their 10-year-old son Philip and their housekeeper Veralicia Figueroa also were killed, and then the house was set on fire with matches and a flammable liquid.

The fire began on the queen-sized mattress where the boy’s body was stabbed and burned, authorities said.