The United States government (plaintiff) prosecuted Lopez Quintero (defendant) for the first-degree murder of his two-year-old daughter, A.B.Q., in violation of 18 U.S.C. § 1111. The trial evidence included Quintero's testimony that his daughter was fatally injured when she fell from the bed of Quintero's parked pickup truck, the testimony of Quintero's wife and son that he regularly beat A.B.Q., the wife's testimony that Quintero initially admitted killing the girl and concocted the truck-bed-fall story only later, and the son's eyewitness testimony that Quintero had been beating A.B.Q. just before she died. A pathologist said it was improbable that even a two-year-old would die from a truck-bed fall. The evidence also showed that, to conceal his crime, Quintero burned A.B.Q.'s body after removing the head and burying it several miles away. The judge granted Quintero's motion for acquittal as to first-degree murder, and the jury acquitted Quintero of second-degree murder despite the government's argument that Quintero must have killed A.B.Q. with malice, because no two-year-old could provoke the sudden quarrel or heat of passion needed to commit the lesser crime of voluntary manslaughter. The jury convicted Quintero of voluntary manslaughter, in violation of 18 U.S.C. § 1112. Quintero appealed to the Ninth Circuit Court of Appeals, contending that the government failed to prove that he acted upon a sudden quarrel or heat of passion, and therefore he could be convicted of nothing more serious than involuntary manslaughter.