Or, hear me out, the "delayed" arrests are so they don't make mistakes that would result in a mistrial because they don't want you to jump up and yell "they intentionally violated their rights so the judge would throw the case out".
There was more than enough probable cause for arrest, and after the perp has been arrested, prosecution has 72 hours to build a case and press charges. This is just more of the usual, also because the career of the prosecutor depends on the goodwill of the cops.
