Because this isn’t TV land. An investigation needs to cross the t’s and dot the i’s. Cellphone saying it (and probably you) were there doesn’t mean you did it. What that does is tell them to see if your prints or DNA are on record and can be matched with evidence found at the scene. Which of course has to have been found and processed. I’ve got a friend who spent a career working in the blood evidence lab. She hates those shows, and a big part of why she hates them is because they make people ask the same question you did. None of the process is fast. And you don’t actually want it to be fast. Fast is sloppy, sloppy is bad, sloppy destroys evidence, sloppy breaks evidence chains and loses cases, sloppy makes the wrong people go to trial. Their job is to be thorough, be careful, and make sure they don’t botch the case. All of which takes time.
Well stated.
Worst of all, sloppy gets the case dismissed by the judge and the defendant set free.
Reminds me of the OJ Simpson case. A lot of the evidence was mishandled, there was sloppiness, and as a result he got off.