In what circumstances will a police officer stop and detain a man who is about to leave the scene of crime?

In Jones, an officer in a patrol car saw a small group of men standing on a street corner. He noticed one man hand some money to the defendant. Deciding he would investigate, he turned his patrol car across the opposing lane of traffic, stopping it at a diagonal to the corner about 10 feet from the men. He then got out of the car, but the defendant started to walk away. The officer told the defendant to stop. (People v. Jones, supra, 228 Cal.App.3d at pp. 521-522.) Not having any information "causing [the officer] to suspect that (1) some activity relating to a crime has taken place, is occurring, or is about to occur; and (2) the person he intends to stop or detain is involved in that activity[,]" the appellate court found the conduct of the officer was unjustified. No reasonable person in that situation would have felt he or she had the ability to merely walk away. (Id. at pp. 523-524.)