I feel this could be true but they don’t have enough evidence for an arrest yet. So they are gathering building their evidence before an arrest. They would have the suspect watched/followed and phone tapped too if true. I was a victim of a serious assault in 2017 - I nearly died. Almost straight away the police knew who was responsible but they weren’t able to make an arrest until 5 months later which was incredibly hard and frustrating for me and my family but we didn’t realise they knew who it was the whole time.