felt that he could also survey the area and see who else was around and what the chances were that this was a law enforcement operation. >> in fact, the long beach police have the park surrounded. we're there with our cameras. according to his chat, sierras is driving an suv. but suddenly, he drives up in a different vehicle and approaches the decoy. >> hey i look this way cause that's what i am so -- >> the conversation is hard to hear, but he's clearly suspicious. the decoy's hair looks different from the online photos sierras saw. >> i dyed my hair. since sthat picture. >> as i walk over to talk to him, he spots me and runs. >> he's running. >> the police make their move. >> get down! get down on the ground! get down on the ground. >> stop it. >> all right, all right. >> just do what we tell you. >> who are you? >> we're the police. >> frank, i'm chris hansen with "dateline nbc."