I do wonder if this was something that Dulce did often with her brother and mother, where she and her brother were somewhat alone at the playground while the mother sat in her car in the parking lot paying attention to something else (like her sister's homework). If that's the case, then the suspect could have planned where to park, where to drive, how to evade detection, and how to lure Dulce. In fact, the suspect may have spoken to her in the past. However, we don't know whether this is the first time this happened, or whether it happened often.