What is the current state of the law on the basis of reasonable investigation of suspicious activity by the police?

In reviewing several cases involving the subject at hand, the court in People v. Cowman, 223 Cal.App.2d 109, 117, 35 Cal.Rptr. 528, 534, states: 'The rationale of all these decisions is that an officer of the law, employed to maintain the peace and to prevent crime, as well as to apprehend criminals after the fact, has both the right and the duty to make reasonable investigation of all suspicious activities even though the nature thereof may fall short of grounds sufficient to justify an arrest or a search of the persons or the effects of the suspects. Experienced police officers naturally develop an ability to perceive the unusual and suspicious which is of enormous value in the difficult task of protecting the security and safety of law-abiding citizens. The benefit thereof should not be lost because the cold record before a reviewing court does not contain all the particularized perceptions which may have been so meaningful at the scene.'