Agreed if the police have evidence putting PR at the park then the bench story could just be a fabrication to suit his purposes , or they might even really have sat together on the bench before things took a down turn.Unless, as we suspect, they have some evidence putting P at that park, and the sister’s story about him giving “a crying girl” a lift is true, in which case he may have concocted some bench story in his defence
But if the police are sure based on irrefutable evidence above and beyond just PR that the park is the location then i would have expected a more comprehensive search, jmo. I dont feel the police are sure at all.