A newborn girl found dead in a Bronx courtyard Monday was likely thrown from an apartment window, police sources said.

The infant, its umbilical cord still attached, was found at 2:40 p.m. behind a six-story residence at Sedwick Avenue and West 183rd Street in University Heights.

“Whoever did that should be executed,” said a neighbor, who gave his name as Nelson.

“That baby didn’t even get to enjoy life. Whoever did . . . that must be out of their mind or high on drugs.”

Cops were questioning the baby’s 33-year-old mother last night. They were also talking to a man believed to be her boyfriend.