In Green v. Department of Motor Vehicles (1977) 68 Cal.App.3d 536, a citizen who had observed the defendant driving her car in an erratic manner followed her to her home where she parked the car, then located a police officer to whom he reported his observations. Thinking "he had done all he need do," the citizen then went home. (68 Cal.App.3d at pp. 539, 541.) Rejecting the contention that the police exceeded their authority in ordering the defendant out of her car and administering field sobriety tests before the citizen-witness, whom they had called back to the scene, arrived and "uttered the magic words of arrest" ( id., at p. 542), the court stated: "The police were acting as agents assisting in effectuating the citizen's arrest, . . . The entire sequence of events beginning when the citizen decided to arrest respondent and went to get help constitutes the arrest ." (Ibid.)