I am writing something that involves a criminal (wanted for robbery and a high body count spree killing) on the run from the law in America. I'm British and struggling a little to work out a few little details on how the law works. I've tried googling but the topic is so vast that I just can't get to what I need. I think it's a basic lack of understanding that's the problem. The cops pursuing this criminal are not remotely the main focal point of the book (which is fairly light/comedic in tone) but I do need cops on his tail throughout in order to propel the plot. I just don't want to have some kind of gaping hole in it that Americans will read and think "what? This isn't how it works at ALL!" - bear in mind, I'm not writing "The Wire" here but I want them to at least act a little like real cops
Basically, the criminal (who is a resident of St Louis, Missouri and has a list of prior offences there (for which he's served time)) commits the first of his crimes - a significant spree killing - in Madison County and the Sheriff there picks up the case. The criminal is on the run and soon crosses state lines - he's heading to Mexico (naturally). Other police departments are notified that he's on the run and he is stopped by a traffic cop in Tennessee. He kills again in Little Rock and moves on to Dallas and, eventually, Roswell, New Mexico.
I want the Sheriff from Madison County to be involved in this manhunt but I'm guessing he wouldn't be allowed to head this up. Would the case go Federal if it crossed state lines? If so, what are the odds of the Federal Agent letting the Sheriff stay involved?
I know I'm opening a can of worms here and maybe asking too complexed a question but just some basic guidelines on how this works would be much appreciated.