What is the "knowledge element" of a stolen property claim?

"The knowledge element of receiving stolen property is normally proved not by direct evidence but by an inference from circumstantial evidence." (People v. Alvarado (1982) 133 Cal.App.3d 1003, 1019.) The knowledge element may be "inferred from the defendant's failure to explain how he came to possess a stolen item or his offer of an unsatisfactory explanation or from suspicious circumstances attendant upon his possession of the item." (Id. at pp. 1019-1020.)