What is the burden of proving provocation in a murder case?

"[I]n a murder case, unless the People's own evidence suggests that the killing may have been provoked . . . , it is the defendant's obligation to proffer some showing" on provocation sufficient to reduce a killing to manslaughter. (People v. Rios (2000) 23 Cal.4th 450, 461-462.) "If the issue of provocation . . . is thus 'properly presented' in a murder case [citation], the People must prove beyond reasonable doubt that these circumstances were lacking in order to establish" the malice element of murder. (Id. at p. 462.) Appellant contends that the prosecution's evidence "properly presented" or suggested provocation, and therefore the prosecution had the burden of proving an absence of it.