Why do some major cases go to trial quickly while?

others drag on forever? The OJ trial happened within a year of Nicole's death while in the Caylee Anthony case, her remains were found in 2008, while the trial won't happen until 2011. This case was on the news heavily now has died down some. Do some trials happen right away because the public presses it? Like with the OJ case, the public kept on it. Why do some cases go to trial almost immediately while others, it takes years?